MAG arc welding apparatus

ABSTRACT

An MAG arc welding method and apparatus is capable of achieving a welding bead in a regular ripple pattern or in a suitable sectional form. The welding power source generates the first welding current I1 and a second welding current I2 larger than the first welding current. The wire melting speed is changed by switching between the first and the second welding currents. The welding method or apparatus according to the invention generates the first arc length more than 2 mm and the second arc length more than the first arc length and switches between both arc length at a switching frequency F of 0.5 to 25 Hz. The ratio of the second to the first welding currents is made to be in 1.03 to 1.20. In addition to a welding method to change the arc length by switching the first and the second welding currents at a constant wire feeding rate, the present welding method makes it possible to carry out the lap welding or butt welding even when there is a large gap. The large gap requires a large amount of molten metal which is prepared by increasing the wire melting speed caused by an increase in the wire feeding rate by 5 to 20%. The resultant reinforcement has a beautiful appearance.

This is a divisional of application Ser. No. 07/778,845 filed on Dec.13, 1991, now U.S. Pat. No. 5,508,493.

FIELD OF ART

The present invention relates to a method and apparatus for pulse MAGarc welding which can obtain a welding bead having a regular waveformappearance or showing an appropriate cross-sectional shape.

BACKGROUND OF THE ART

In the recent years, aluminum and aluminum alloy (referred to analuminum herein after) have been used widely for interior materials ofbuildings, various vehicles and transportation machines. Welded jointsof these aluminum used in the above fields form directly an outsideappearance and hence are required to have a beautiful appearance of thewelding beads in addition to a sufficient mechanical strength. As an arcwelding method showing a beautiful appearance of welding beads, a widelyused method is a TIG arc welding method having a filler wire addedthereto. The welded joint obtained with a TIG arc welding having thefiller wire added thereto (referred to a TIG filler arc welding methodhereinafter) shows a bead appearance in regular wave form (referred to ascale bead hereinafter) as shown in FIG. 1. The welding bead accordingto the TIG filler arc welding method has an appearance more beautifulthan that of the MIG arc welding method.

The TIG arc welding method is lower in the welding speed than that ofMIG arc welding method which melts the consumable electrode and is in alower production efficiency. Therefore, various proposals have beenconducted to a method in which the MIG arc welding method could be ableto achieve the welding bead appearance near to the scale bead due to theTIG arc welding method having the filler wire added thereto.

Prior Art 1

The prior art 1 is a MIG arc welding method disclosed in the JapanesePatent Publication (examined) Syo 46-650 and is to change alternativelythe arc spray amount between the high value and the low value. In orderto actually execute this method, the electric power supplied to the arcis alternatively changed between the relatively high value andrelatively low value (for example 3:2).

FIG. 2 shows a block diagram of an electric source for use in thiswelding method. FIG. 3 is a graph showing a V-I characteristic betweenan output current (horizontal axis) and an output voltage (verticalaxis) (referred to V-I characteristic hereinafter) and an arccharacteristic. With reference to FIG. 2, a reference numeral 101denotes an output circuit for welding electric source; a referencenumeral 102, a resistor for switching the V-I characteristic of theoutput circuit for welding electric circuit 101; a reference numeral103, a contact for shortcircuiting and opening the resistor 101; and areference numeral 104, a timer for switching periodically the contact103. A reference numeral 1 denotes a consumable electrode wire (referredto a consumable electrode hereinafter) transferred to a welding material2 through an electric supplying tip 4 at a predetermined speed by a wiresupplying motor WM. An arc 3 is generated between the consumableelectrode 1 and the welding material 2 and is to weld the weldingmaterial 2.

FIG. 3 shows a V-I characteristic AA applied between the consumableelectrode 1 and the welding material 2 when the resistor 102 isconnected to the output circuit, a V-I characteristic BB when theresistor 102 is short circuited and an arc characteristic at arc lengthsof L1 to L3 shown by dotted lines L1 to L3. It is assumed that anoperation point is a crossing point A of a solid line AA and a dottedline L1 of FIG. 3 when the consumable electrode 1 is transferred atpredetermined value of wire supplying speed WF1. At this time, a weldingelectric current is in I1 and an arc voltage is in V1.

There are three methods for switching the above electric power.

(1) A first method is to switch an output voltage supplied across theconsumable electrode 1 and the welding material 2. For example, in FIG.3, when the V-I characteristic is switched from AA to BB, the weldingelectric current I1 does not change but the operation point movesusually to B point of the V-I characteristic curve BB because the wiresupplying speed and the welding electric current are not proportionalperfectly to each other. However, at the transient time, the arc lengthL1 does not rapidly change with the rapid change in the V-Icharacteristic curve into the BB curve. Therefore, the operation pointmoves from a point A on the arc characteristic curve L1 the same as theabove curve to a point D. The movement causes an increase in the weldingelectric current and then an increase in the wire melting speed whichresults in an increase in the arc length. Then, the arc length changesfrom the curve L1 to an arc characteristic curve L2 having a long arclength and finally moves to a point B. Therefore, the welding currentchanges largely from I1 to I3 at a transient state and from I1 to I2 ata stationary state.

(2) A second method is to switch the wire supplying speed. For example,in FIG. 3, when the wire supplying speed is switched, the switching iscarried out so as to change the arc length on the V-I characteristic AAand hence the operation point changes from a point B to a point C.Accordingly, the welding electric current changes largely from I2 to I4and the arc length moves from the operation point of the arccharacteristic curve L2 to the operation point of the curve L3.

(3) A third method is to change the V-I characteristic of above case (1)and the wire supplying speed at case (2) simultaneously. Accordingly,the welding electric current changes largely from I1 to I4.

Prior Art 2

The prior art 2 is a MAG welding method described in Japanese PatentPublication (examined) Sho 49-48057 and is to supply the consumableelectrode at a predetermined speed by using a constant voltagecharacteristic of a welding electric source. The welding methodaccording to prior art 2 is to change periodically the welding electriccurrent and simultaneously change the welding wire supplying speed witha change in the welding electric current. That is, this method is toswitch between a high electric current (a high output voltage) due to ahigh speed of wire supplying and a low current (a low output voltage)due to a low speed of wire supplying and to control input heat. FIG. 4(A) to (C) are graphs showing V-I characteristic curves AA and BBbetween the output current of the welding electric source (horizontalaxis) and the output voltage (vertical axis) and arc characteristiccurves L1 and L2.

There are three practical methods for controlling the input heatmentioned above.

(1) A first method is not to change the arc length at both of the highelectric current and the low electric current. As shown in FIG. 4 (A),for example, when the both of the V-I characteristic of the weldingelectric source and the wire supplying speed are switched, the operationpoint moves from the operation point A at the crossing point of the V-Icharacteristic curve AA and the arc characteristic curve L1 to theoperation point B of the crossing point of the V-I characteristic curveBB and the arc characteristic curve L1. At this time, the weldingcurrent changes largely from I1 to I2 while the arc length is L1 on thesame curve does not change.

(2) A second method is to change in a larger degree the wire supplyingspeed than the case (1) when the arc length does not change. That is,with a high electric current, the wire supplying speed is made higherand the arc length is made shorter while with a low electric current,the wire supplying speed is made low and the arc length is longer. Forexample, as shown in FIG. 4 (B), when the wire supplying speed isswitched, the operation point moves from the crossing point A of the V-Icharacteristic curve AA and the arc characteristic curve L2 to thecrossing point B of the V-I characteristic curve AA and the arccharacteristic curve L1. In this time, the welding current changeslargely from I1 to I2 while the arc length changes from L2 to L1.

(3) A third method is to change the wire supplying speed in a smallerdegree than the case (1) where the arc length does not change. At thehigh electric current, the wire supplying speed is made low and the arclength is made long while at the low electric current, the wiresupplying speed is made high and the arc length is made short. Forexample, as shown in FIG. 4 (C), when both of the V-I characteristic ofthe welding electric source and the wire supplying speed are switched,the operation point at the stationary state moves from the crossingpoint A of the V-I characteristic curve AA and the arc characteristiccurve L1 to a crossing point B of the V-I characteristic curve BB andthe arc characteristic curve L2. However, at the transient state, evenwhen the V-I characteristic curve changes rapidly into the curve BB, thearc length does not rapidly change. However, the operation point movesfrom the point A to the point D with the same arc length to each other,while the welding electric current increases. As a result, the wiremelting speed is also higher and the arc length is longer. The arclength moves from the curve L1 to the curve L2 and finally the operationpoint moves to the point B. Therefore, the welding electric currentchanges largely from I1 to I3 at the transient state and from I1 to I2at the stationary state.

Prior Art 3

The prior art 3 is a pulse MIG welding method described in the JapanesePatent Publication (unexamined) Syo 62-279087 and is to switch a basecurrent or base voltage switch between a spray transfer and a shortcircuit transfer to form a scale bead without melting down aluminum thinplate.

(1) For example, as shown with a wave form of a welding electric currentin FIG. 5 (A), the use of a pulse welding electric source comprising aconstant pulse current in which either of pulse current, pulse width orpulse frequency is a constant value and a variable base current permitsthe spray transfer and the short circuit transfer to be carried outalternatively by changing the base current periodically in a largedegree.

(2) As shown with a wave form of a welding voltage in FIG. 5 (B), theuse of a pulse welding electric source outputting a welding voltagecomposed of a pulse voltage in which either of a pulse voltage, pulsewidth or pulse frequency is a constant value and variable base voltagepermits the spray transfer and the short circuit transfer to be carriedout alternatively by changing the base voltage periodically in a largedegree.

Accordingly, this prior art 3 switches the wire feed rate as shown inFIG. 5(A) and hence changes periodically the average value of weldingcurrent in a large scale by changing the welding current values into anaverage value H1 at the high current period T8 and the average value N1at the low current period T9. Thus, it is possible to switch between thespray transfer and the short circuit transfer. Further this prior art 3switches the output power of the base electric source in a large scaleas shown in FIG. 5(B). In the method shown in FIG. 5 (B), the weldingcurrent value changes in a small scale at the stationary state butchanges in a large scale at the transient state in a similar way to thatof the prior art 1.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Problem of Prior Art 1

In a welding method according to prior art 1, it is necessary to switchalternatively the arc spray value between a high value and a low valueat a current range higher than the critical current Ic necessary for thespray transfer. Accordingly, the wire feed rate must be switched at thesame time and thus the welding current 12 necessary for obtaining a highvalue of the arc spray amount is comparatively higher than the criticalcurrent Ic. This prevents the welding method according to the prior art1 from welding a thin plate.

Further, the welding method according to prior art 1 manages the weldingcurrent to change relatively in a large scale (for example 2:3) and canbe applicable for a working step such as a step to change the arc forcein a large scale, to change the penetration depth or to change theamount and the shape of the reinforcement by changing the amount of thedeposited metal. However, the welding method according to the prior art1 is not suitable for the method for obtaining a bead appearance of themolten pool surface, for example, a scale bead with a constant size ofthe penetration depth and the reinforcement. The method described aboveis an object of the present invention. As a result, the welding methodaccording to the prior art 1 shows a bead appearance shown in FIG. 6 andcan not achieve the beautiful scale bead having a regular ripple patternas shown in FIG. 1 in connection with the TIG filler arc welding method.

Problem of Prior Art 2

The welding method according to the prior art 2 changes the weldingcurrent in a large scale (in the embodiment, 260 A! and 100 A!, 90 A! or60 A!) to control the input heat by switching periodically the outputvoltage of the welding electric source of constant voltagecharacteristic and the wire feed rate.

Therefore, in a similar way to that of the welding method according tothe prior art 1, the welding method according to the prior art 2 managesthe welding current to change relatively in a large scale and can beapplicable for a working step such as a step to change the arc force ina large scale, to change the penetration depth or to change the amountand the shape of the reinforcement by changing the amount of thedeposited metal. However, in a similar manner to the welding methodaccording to the prior art 1, the welding method according to the priorart 2 is not suitable for the method at which the present inventionaims.

Problem of Prior Art 3

The welding method according to the prior art 3 is to changeperiodically the base current or the base voltage in a large scale toswitch between the spray transfer and the short circuit transfer whilekeeping constant values of either of pulse current, pulse voltage, pulsewidth or a pulse frequency. Finally, the welding method according to theprior art 3 is to achieve the scale bead without melting down a thinplate of aluminum.

However, the welding method according to the prior art 3 manages theswitching between the spray transfer and the short circuit transfer tobe repeated periodically. During the short circuit transfer, the headingterminal of wire is in contact with the molten pool to carry out themetal transfer. As a result, the bead appearance by the welding methodaccording to the prior art 3 is the same as that shown in FIG. 6 in asimilar way to that of the welding method according to the prior art 1and does not show the scale bead as shown in FIG. 1.

When the above welding methods are adapted for the present invention,there appears at least one problem described below.

(1) When the short circuit transfer is carried out, a large grain of themolten metal is transferred irregularly.

The conventional MIG arc welding method is to change the wire moltenamount by changing largely the average value of the welding current withthe switching of the wire feed rate. An aluminum alloy A-5183 plate in athickness of 4 mm is welded by the MIG arc welding method based on theswitching between the spray transfer and the short circuit transferunder the following welding conditions; electrode, aluminum alloyconsumable electrode A-5183 of thickness of 1.2 mm; switching period, 2Hz between a first setting condition of welding current 90 A and weldingvoltage 19 V and a second setting condition of welding current 180 A and21 V; welding voltage 21 V; and a welding speed, 40 cm/min. As a result,the bead appearance so obtained is the same as that shown in FIG. 6 anddoes not show a beautiful scale bead having a regular ripple patternobtained with the TIG filler arc welding method as shown in FIG. 1.

Specially, in the high speed welding with a thin plate, it is necessaryto decrease the welding current in addition to increase the pulseswitching frequency more than 3 Hz. Hence, it is possible to set thesecond welding condition at the welding current necessary for the spraytransfer. However, the first condition is to set the welding current ina small size which permits no spray transfer but the short circuittransfer. As a result, a large grain of molten metal at the heading endof the wire is in contact with the molten pool and hence it is difficultto make the welding bead to be in a scale bead obtained with the TIGfiller arc welding method.

(2) When the wire feed rate is switched, the response time is low due tothe mechanical inertia.

On the other hand, in connection with the welding of thin plate at ahigh speed, it is necessary to elevate the switching frequency betweenthe first welding condition setting value and the second weldingcondition setting value in response to the welding speed. Otherwise, theweld beads are different in the height and width between the area wherethe molten metal transfers and the area where the molten metal does nottransfer. However, in a conventional MIG arc welding method to changelargely the average value of the welding current, it has been necessaryto switch the wire feed rate in a large degree. Hence, the response timeis made low by the mechanical inertia of a wire feed motor and feedmechanism, and the switching frequency is only 3 HZ. In addition, themechanical inertia causes the boundary of switching uncertain. As aresult, it is difficult to obtain the scale bead having a regular ripplepattern as shown with the TIG arc welding method.

(3) The welding current has a large variation value.

In the conventional welding electric source, the welding current variesin a large degree upon the switching of the wire feed rate, because ofthe constant voltage characteristic of both the first welding conditionand the second welding condition. Further, upon the switching of theoutput voltage of the welding electric source, the welding currentvaries in a large degree at the transient state because of the constantvoltage characteristic. With the large variation in the welding current,there is a large variation in the arc strength, in the penetrationdepth, or in the height and the shape of the reinforcement due to thevariation in the amount of the deposited metal. As a result, it is notpossible to change only the surface of the molten metal.

(4) When the wire feed rate is switched, the variation in the arc lengthis low.

In order to keep the welding at the constant arc length with the MIG orMAG arc welding method, it is necessary to hold the following equationin a principle way.

    wire feed rate=wire melting speed                          (1)

(The wire melting speed is a function of the welding current value.)

In a welding electric source having a constant voltage characteristic,the welding current varies with the variation in the wire feed rate asdescribed above. The welding current is approximately proportional tothe power of 1.05 to 1.5 of the wire feed rate depending upon thevariation in the quality of the consumable electrode or the arc lengthetc.

In the equation (1), the variation in the arc length can be achieved bythe variation in the wire feed rate or wire melting speed, that is, thewelding current. However, in the welding electric source having aconstant voltage characteristic, since the welding current is determinedby the wire feed rate, only the welding current is not set previouslywith the constant speed of the wire feed rate. Accordingly, in thewelding electric source having a constant voltage characteristic, amethod to change the wire feed rate is adopted first. The change in thewire feed rate results in the change in the wire melting speed resultingfrom the change in the welding current. As a result, the variation inthe arc length is low.

Further, a method to change the output voltage with the change in theV-I characteristic of the welding electric source having a constantvoltage characteristic determines the arc length by the output voltageand the welding current when the wire is fed at a constant speed.Accordingly, it is not possible for this method to change the arc lengthby the direct control of the welding current.

Means For Solving The Problem

An object of the present invention is to provide a MAG arc weldingmethod and a welding apparatus capable of solving any of the problemsaccompanied with the welding method or apparatus known in the prior artand being characterized by the following features:

(1) no short circuit transfer;

(2) no switching of the wire feed rate in principle;

(3) no large variation in the welding current; and

(4) switching periodically the wire melting speed, that is, the weldingcurrent by a small amount in view of the equation, (wire feedrate)=(wire melting speed).

Switching the output current of the welding electric source

A principle of the present invention is to change largely the arc lengthby switching the welding output current of the welding electric sourcewithout changing the wire feed rate. A process to set or control theswitching output current can suppress the variation in the outputcurrent at the transient state within the tolerance of 10%. As a result,it is possible to make the transferring grains of the molten metal to bein a uniform size and to prevent the short circuit due to the largegrain size of the molten metal even with the short arc length. Further,in the present invention, it is possible to elevate the switchingfrequency F to 25 Hz without changing the wire feed rate.

In the welding electric source according to the prior art, the weldingoutput voltage only can be switched but the welding current itself cannot be switched. It is possible to change the output current due to theself controlling effect of the V-I characteristic of the weldingelectric source by switching the wire feed rate with an use of weldingelectric source having constant voltage characteristic. Accordingly, itis not possible for the welding electric source having the constantvoltage characteristic according to the prior art to set or control theoutput current value of the welding electric source. Therefore, it isnot possible for the prior art to set or control the variation value ofthe output current in a manner as shown by the present invention.

The present invention is to provide a welding method to change the arclength by switching the welding output current without changing the wirefeed rate (referred to a basic welding method hereinafter). In additionto the basic welding method, the present invention is to provide anotherwelding method described in the following. When the basic welding methodis applied for the butt welding or the lap welding described later, itis possible for the basic welding method to carry out welding even withthe large gap. In such a case, since the molten metal to fulfill the gaplacks, the reinforcement can be obtained by increasing the wire feedrate by 5 to 20% and then increasing the wire melting speed. Thiswelding method is referred to an additional welding method hereinafter.

A welding method described herein is a MAG arc welding method (referredto MAG welding method hereinafter) comprising the following steps of; astep of changing a wire melting speed by switching, at a switchingfrequency of F=0.5 to 25 Hz, a welding current between a first weldingcurrent I1 and a second welding current I2 larger slightly than thefirst welding current I1; a step for changing periodically an arc lengthbetween a first arc length Lt larger than arc length of 2 mm and asecond arc length Lr larger than the first arc length; and a step forholding a ratio of the second welding current I2 to the first current I1to be 1.03 to 1.20.

The MAG welding method further comprises a step for switching betweenthe first welding current I1 and the second welding current I2 at aswitching frequency F; and a step for holding a variation value Lebetween a first voltage Val at the first arc length Lt and a secondvoltage Va2 at the second arc length Lr to be 0.3 to 4.0 V.

The MAG welding method further comprises a step for supplying a firstwelding current carrying out a spray transfer to generate a small shortcircuit at a first arc length from a welding output controlling circuitfor outputting a direct current having a constant current characteristicand a step for supplying a second welding current carrying out a spraytransfer not to generate a small short circuit at a second arc lengthfrom a welding output controlling circuit outputting a direct currenthaving a constant current characteristic in a similar way to the above.

The MAG welding method further comprises a step for supplying a firstwelding current carrying out a spray transfer to generate a small shortcircuit at a first arc length from a welding output controlling circuitfor outputting a group of pulse currents and a step for supplying asecond welding current carrying out a spray transfer not to generate asmall short circuit at a second arc length from a welding outputcontrolling circuit for outputting a direct current having a constantcurrent characteristic.

The MAG welding method is further characterized in that said firstwelding current for obtaining said first arc length is a first group ofpulse currents and said second welding current for obtaining said secondarc length is a second group of pulse currents.

The MAG welding method further comprises a step for making a graphhaving a vertical axis composed of a variation value Le mm between saidfirst arc length Lt and said second arc length Lr and a horizontal axiscomposed of switching frequency F=0.5 to 25, a step for determining, onsaid graph, specified positions of a first position at the switchingfrequency F=0.5 Hz and the arc length variation value Le=2.5 mm, asecond position at the switching frequency F=12 and the arc lengthvariation value Le=1.0 mm and a third position at the switchingfrequency F=25 Hz and the arc length variation value Le=0.5 mm, and astep for carrying out the welding by using the arc length variationvalue Le and the switching frequency F Hz on said graph positioned upperthe curves obtained by connecting said first, said second and said thirdpositions to each other.

The welding apparatus for carrying out the method described above isembodied as a pulse MAG welding apparatus capable of switchingperiodically, with a switching signal, between a first group of pulsecurrents for obtaining a first arc length Lt and a second group of pulsecurrents for obtaining a second arc length Lr, wherein the apparatuscomprises:

an arc voltage detection circuit VD for outputting an arc voltagedetection signal upon detection of an arc voltage;

an arc voltage controlling circuit including a comparator CM2 foroutputting an arc voltage controlling signal Cm2 corresponding to adifference between an arc voltage detection signal Vd and a switchingarc voltage signal S6 for switching between a first arc voltage settingsignal Vs1 and a second arc voltage setting signal Vs2;

a pulse base current controlling circuit for outputting a pulse basecurrent controlling signal to control a pulse frequency f3, a pulseduration TP3, a base current IB3 or a pulse current TP3 corresponding toan arc voltage controlling signal Cm2;

a first pulse base current setting circuit for outputting a first pulsebase current setting signal by setting three conditions excluding acondition to control with a pulse base current controlling signal fromfour conditions of a pulse current value, a pulse duration, a pulsefrequency and a base current value of a first group of pulse currents;

a second pulse base current setting circuit for outputting a secondpulse base current setting signal by setting three conditions excludinga condition to control with a pulse base current controlling signal fromfour conditions of a pulse current value, a pulse duration, a pulsefrequency and a base current value of a second group of pulse currents;

a switching circuit HL for outputting a switching signal H1 by switchingat a switching frequency F=0.5 to 25 Hz;

at least one switching setting circuit for outputting a switching arcvoltage signal S6 to switch, with a switching signal H1, between a firstarc voltage setting signal Vs1 and a second arc voltage setting signalVs2, a switching setting signal to switch, with a switching signal H1,between a first pulse base current setting signal and a second pulsebase current setting signal or both of said switching arc voltage signalS6 and said switching setting signal;

a pulse control signal generator circuit for outputting a first pulsecontrol signal Pf1 and a second pulse control signal Pf2 upon receivinga pulse base current control signal and a switching setting signal; and

a welding output control circuit for outputting a first group of pulsecurrents upon receiving a first pulse control signal Pf1 and a secondpulse control signal Pf2 upon receiving a second pulse control signalPf2.

The welding apparatus described above is further based on a pulse MAGwelding apparatus wherein said pulse base current control circuit foroutputting a pulse base current control signal is a pulse frequencycontrol signal generator circuit VF3 for outputting a pulse frequencycontrol signal Vf3 to control a pulse frequency f3, and said first pulsecurrent setting circuit for outputting a first pulse base currentsetting signal comprises a pulse value setting circuit IP1 for setting apulse current setting signal Ip1, a pulse duration setting circuit TP1for setting a pulse duration setting signal Tp1 and a base current valuesetting circuit IB1 for setting a base current setting signal Ib1.

The welding apparatus described above is further based on a pulse MAGwelding apparatus wherein said pulse base current control circuit foroutputting a pulse base current control signal is a comparator circuitCM2 for outputting an arc voltage control signal Cm2 to control a pulseduration, and said first pulse current setting circuit for outputting afirst pulse base current setting signal comprises a pulse current valuesetting circuit IP1 for setting a pulse current value setting signalIp1, a pulse frequency setting circuit FP1 for setting a pulse frequencysetting signal Fp1 and a base current setting circuit IB1 for setting abase current setting signal Ib1.

The welding apparatus described above is further based on a pulse MAGwelding apparatus wherein said pulse base current control circuit foroutputting a pulse base current control signal is a base current controlcircuit IB3 for outputting a base current control signal Ib3 uponreceiving an arc voltage control signal Cm2, and said first pulsecurrent setting circuit for outputting a first pulse base currentsetting signal comprises a pulse current value setting circuit IP1 forsetting a pulse current value setting signal Ip1, a pulse durationsetting circuit TP1 for setting pulse duration setting signal Tp1 and apulse frequency setting circuit FP1 for setting a pulse frequencysetting signal Fp1.

The welding apparatus described above is further based on a pulse MAGwelding apparatus wherein said pulse base current control circuit foroutputting a pulse base current control signal is a pulse current valuecontrol circuit IP3 for outputting a pulse current value control signalIp3 upon receiving an arc voltage control signal Cm2, and said firstpulse current setting circuit for outputting a first pulse base currentsetting signal comprises a pulse duration setting circuit TP1 forsetting a pulse duration setting signal Tp1, a pulse frequency settingcircuit FP1 for setting a pulse frequency setting signal Fp1 and a basecurrent setting circuit IB1 for setting a base current setting signalIb1.

The pulse MAG welding apparatus further comprises a first wire feed ratesetting circuit IM1 for outputting a wire feed rate setting signal Im1,a second wire feed rate setting circuit IM2 for outputting a second wirefeed rate setting signal Im2 and a wire feed rate switching circuit foroutputting a switching wire feed rate signal S7 to a wire feed ratecontrol circuit WC by switching, at a switching frequency F=0.5 to 5 Hz,between said first feed rate setting signal Im1 and said second wirefeed rate setting signal Im2.

Operation

Description of FIG. 7

FIG. 7 is a structural model view showing a variation in the expansionof an arc 3 when an arc length Left and right or Lt varies. In FIG. 7,the arc 3 expands between a wire terminal 1a or 1b of a consumableelectrode 1 supplied with a power from a terminal 4a of the powersupplying tip 4 and welding material 2. In an arc welding of aluminum,the arc transfers easily to an area having an oxide film of aluminum asa welding material 2 from the terminal of the consumable electrode.Hence, the actual arc length L11 or L21 is longer than apparent arclength Left and right or Lt which is a shortest distance between theterminal 1a of wire and the surface of the welding material 2. When thewire projection is in a length of Ln, the apparent arc length is Leftand right. However, the actual arc length is L21 at the maximum. Next,when the wire projection is Lm in the length, the apparent arc length(referred to arc length hereinafter) is Lt but actually L11. In such away, in aluminum welding material, the arc easily moves to the oxidefilm and the aluminum plate has a high cooling speed resulting from thelow melting point of aluminum. A periodical variation in the arc lengthbetween Lt and Left and right causes the actual arc length to changeinto a first arc length L11 and a second arc length L21. With a changein the actual arc length, the size of a molten pool can be directlychanged. (This is different from the conventional art in which themolten pool is indirectly changed by an molten amount of wire and an arcforce.) Accordingly, it is possible for the MAG arc welding methodaccording to the present invention to obtain a scale bead having regularripple pattern in a similar way to that of TIG filler arc weldingmethod.

In FIG. 7, a variation value in the wire projection length between thefirst welding condition setting value and the second welding conditionsetting value or the variation value Le in the arc length is expressedby the following equation; Le=Left and right-Lt=Lm-Ln. Further it isnoted that the arc length Lt and Left and right in FIG. 7 are positionedon the characteristic curves L1 and L2 in FIG. 8 as described later.

Description of FIG. 8

A basic welding method according to the present invention is to changethe arc length by changing the wire melting speed by switching theoutput current value of the welding electric source while keeping thewire feed rate constant. The following explains the basic weldingmethod.

FIG. 8 is conducted to a case where a welding electric source outputtinga direct current in a constant current characteristic supplies a firstwelding current for obtaining a first arc length in a short size and asecond welding electric source outputting a direct current in a constantcharacteristic supplies a second welding current for obtaining a secondarc length in a long size. FIG. 8 is a graph showing a V-Icharacteristic curves CC1 and CC2 and the arc characteristic curves L1and L2 by expressing the output current I of a constant current electricsource at the horizontal axis and the output voltage V at the verticalaxis. With reference to FIG. 8, when the first welding current value I1is switched to a second welding current value I2, the operation pointmoves from a point A on the first arc length L1 in a short size to apoint B on a second arc length L2 in a long size. Thus, the arc voltagechanges from V1 to V2. In this case, a variation value in the weldingcurrent is expressed by the following equation; ΔIa=I2-I1; a variationvalue in the arc voltage, ΔVa=V2-V1, a variation in the arc length,ΔLe=L2-L1.

The description will be directed to a comparison between the weldingmethod according to the present invention shown in FIG. 8 and thewelding method according to the prior art shown in FIGS. 3 and 4. In themovement of operation points A and B in FIG. 8, the variation value inthe welding current ΔIa=I2-I1 can be limited to a value obtained from I2and I1 which are predetermined by the welding electric source having aconstant current characteristic. For example, it is possible to make thefollowing limitation; I2/I1=1.03 to 1.10 according to the basic weldingmethod and I2/I1=1.05 to 1.20 according to the additional weldingmethod. However, in the movement of the operation points A-B, B-C or A-Cshown in FIG. 3 or FIG. 4, it is not possible to set in advance orcontrol the variation value in the welding current. Hence, there appearsa big variation of I1-I2, I1-I3, I1-I4 or I2-I4 with an addition of avariation at the transient state. The next description will be directedto the movement of the operation points A and B in FIG. 8. The variationvalue in the arc length Le=L2-L1 is not limited by a switching range ofthe output voltage of a welding electric source in a constant voltagecharacteristic and can be made in a large variation by enlarging I2/I1because the present method uses a welding electric source having aconstant current characteristic.

It is noted that the operation point C in FIG. 8 is explained withreference to embodiment 5.

Description of FIGS. 9 and 10

FIGS. 9 and 10 indicate the case where a first welding current forobtaining a first arc length in a short size is supplied from a weldingelectric source for outputting a pulse current having a constant currentcharacteristic and second welding current for obtaining a second arclength in a long size is supplied from a welding electric source havinga constant current characteristic the same as that of FIG. 8, which doesnot supply a pulse current.

FIG. 9 is a graph of a welding current obtained by the repetition of afirst welding current of a pulse current PC1 and a second weldingcurrent of a constant current CC2 without a pulse. A reference characterIP1 denotes a pulse current value; a reference character TP1, a pulseduration; a reference character D1, pulse period, that is, an inversenumber of a pulse frequency f1; a reference character IB1, a basecurrent value; a reference character I2, a second welding current value;and a reference character M1, an average value of the welding currentsin a group of pulse currents. It is noted that the various valuesmentioned above have the following relationships.

    D1=1/f1

    I1=M1= IP1×TP1+IB1×(D1-TP1)!/D1

FIG. 10 is a graph showing a V-I characteristic curve of a weldingelectric source outputting a first welding current of a pulse currentPC1 and a second welding current of a constant current CC2 without pulseand the arc characteristic curves L1 and L2 by expressing the outputcurrent I of a constant current electric source at the horizontal axisand the output voltage V at the vertical axis. In FIG. 10, when thepulse current PC1 is switched to the constant current CC2 without pulseunder keeping the wire feed rate at a constant value, the descriptionthe same as that of FIG. 8 can be obtained.

A difference between the welding method according to the presentinvention shown in FIG. 10 and the welding method according to the priorart as shown in FIGS. 3 and 4 is the same description as that of FIG. 8.When the first welding current value I1 is positioned at the vicinity ofthe critical current value Ic, it is possible for the welding methodaccording to the present invention to prevent the short circuit evenwith a first arc length in a short size because the molten metal to betransferred due to a pulse current do not form a large grain.

Description of FIGS. 11 and 12

FIGS. 11 and 12 are graphs illustrating a case where a first weldingcurrent for obtaining a first arc length in a short size and a secondwelding current for obtaining a second arc length in a long size aresupplied, as pulse currents PC1 and PC2, from the welding electricsource.

FIG. 11(A) is a graph showing the time passage of the welding current Icomposed of the repeat of a first pulse current group PC1 and the secondpulse currents group. FIG. 11 (B) is a graph showing the time passage ofa switching signal H1 for switching periodically between a first pulseenergizing period T1 for energizing the first pulse currents group and asecond pulse energizing period T2 for energizing the second pulsecurrents group PC2. A reference character IP1 denotes a pulse currentvalue; a reference character TP1, a pulse duration; a referencecharacter D1, pulse period, that is, an inverse number of a pulsefrequency f1; a reference character IB1, a base current value; areference character T1, a first pulse energizing period; and a referencecharacter M1, an average value of the welding currents during the firstpulse energizing period. It is noted that the various values mentionedabove have the following relationships.

    D1=1/f1

    M1= IP1×TP1+IB1×(D1-TP1)!/D1

Next, a reference character IP2 denotes a second pulse current value; areference character TP2, a second pulse duration; a reference characterD2, a second pulse period, that is, an inverse number of a pulsefrequency f2; a reference character IB2, a second base current value; areference character T2, a second pulse energizing period; and areference character M2, an average value of the welding currents duringthe second pulse energizing period. It is noted that the various valuesmentioned above have the following relationships.

    D2=1/f2

    M2= IP2×TP2+IB2×(D21-TP2)!/D2

FIG. 12 is a graph showing a V-I characteristic curve of a weldingelectric source outputting a first pulse current group PC1 and a secondpulse currents group PC2 and the arc characteristic curves L1 and L2 byexpressing the output current I of a constant current electric source atthe horizontal axis and the output voltage V at the vertical axis. InFIG. 12, when the pulse currents group PC1 is switched to the secondpulse currents group PC2 under keeping the wire feed rate at a constantvalue, the description the same as that of FIG. 8 can be obtained.

A difference between the welding method according to the presentinvention as shown in FIG. 12 and the welding method according to theprior art as shown in FIGS. 3 and 4 is the same description as that ofFIG. 8. When the average value M1 or M2 for the first or secondenergizing period is lower then the critical current value Ic, it ispossible for the welding method according to the present invention toprevent the short circuit even with a first arc length in a short sizebecause the molten metal to be transferred due to a pulse current do notform a large grain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a scale bead in a regular ripplepattern obtained by a conventional TIG filler arc welding method.

FIG. 2 is a block diagram showing the output signal switching circuitfor use in a conventional MIG welding method according to the prior art1 (Japanese Patent Publication (examined) SYO 46-650).

FIG. 3 is a graph showing a V-I curve and the arc characteristic curveof a welding electric source for use in the conventional MIG weldingmethod according to the prior art 1.

FIGS. 4(A) to (C) are graphs showing the V-I characteristic curve andthe arc characters curves for use in the conventional MAG welding methodaccording to the prior art 2 (Japanese Patent Publication (examined) Syo49-48057.

FIGS. 5(A) and (B) are graphs showing a wave form of welding voltageobtained by switching largely the base current with a variation in thewire feed rate through MIG method according to the prior art 3 (JapanesePatent Publication (unexamined) Syo 62-279087) and by switching largelythe base voltage with the variation in the waveform of welding currentobtained by switching the average value of the welding current betweenthe high current and the low current and in the output voltage of thebase electric source.

FIG. 6 is a perspective view showing the appearance of a scale beadhaving no regular ripple pattern formed by the conventional MIG arcwelding method.

FIG. 7 is a structural model view showing the expansion of the arc withthe variation in the arc length performed by a welding method accordingto the present invention.

FIG. 8 is a graph showing the relationship between the V-Icharacteristic CC1 and CC2 of a welding electric source having theconstant current characteristic and the arc characteristic L1 and L2.

FIG. 9 is a graph showing a current obtained with the repeat of thefirst welding current of the pulse current PC1 and the second weldingcurrent of a constant current without the pulse CC2.

FIG. 10 is a graph showing the V-I characteristic curves of the firstwelding current of pulse current PC1 and the second welding current of aconstant current without the pulse and the arc characteristic L1 and L2.

FIG. 11(A) is a graph showing the time passage of welding currentobtained with the repeat of the first pulse currents group PC1 and thesecond pulse currents group PC2; and FIG. 11(B) is a graph showing atime passage of the switching signal for switching the first pulseenergizing period T1 and the second pulse current energizing period T2.

FIG. 12 is a graph showing the V-I characteristic curves of the firstpulse current PC1 and the second pulse current PC2 and the arccharacteristic curves L1 and L2.

FIG. 13 is a graph showing the pulse energizing time and the form of themolten metal transferred corresponding to the pulse energizing time.

FIG. 14(A) is a graph showing the relationship between the average valueof the welding current Ia (horizontal axis) and the average value of thearc voltage Va (vertical axis) obtained when the arc length L variesfrom the first arc length 2 mm which is the shortest length to produce aslight short circuit to the second arc length 12 mm or 15 mm which islongest; FIG. 14(B) is a structural model view showing the arc length L.

FIG. 15 is a graph showing the relationship between the variation valuein the arc voltage ΔVa and the variation in the arc length Le with aconstant value of the wire feed rate in connection with the aluminumwelding.

FIG. 16 is a graph showing a variation in the arc length Le with avariation in the welding current value and the arc voltage value underswitching the wire feed rate in connection with aluminum welding.

FIG. 17 is a graph showing a relationship between a variation in the arcvoltage ΔVa and a variation in the arc length Le at a constant value ofthe wire feed rate in connection with stainless steel welding.

FIG. 18 is a graph showing the variation in the arc length Le with thevariation in the welding current value and arc voltage at various wirefeed rates in connection with stainless steel welding.

FIG. 19 is a block diagram of a welding apparatus effecting the weldingmethod of the present invention.

FIG. 20(A) is a perspective view of a scale bead obtained with weldingmethod according to the present invention; FIG. 20 (B) is a sectionalview showing, in a weld proceeding direction, the penetration depth of abead obtained by the method according to the present invention; FIG. 20(C) is a sectional view showing the penetration depth of the beadobtained by the welding method according to the prior art.

FIG. 21(A) and 21(B) are graphs showing waveforms of welding current foruse in the welding method according to the present invention.

FIGS. 22 (A) and (B) are, respectively, a structural model view showinga time passage of phenomenon to separate the molten metal grain from theterminal of wire when the first pulse currents group carries out the onepulse to one molten grain transfer, and a graph showing the time passageof the energized pulse current of the pulse currents group.

FIGS. 23 (A) and (B) are, respectively, a structural model view showinga time passage of phenomenon to separate the molten metal grain form theterminal of wire when the first pulse currents group carries out aplurality of pulses to one molten metal grain transfer, and a graphshowing the time passage of the energized pulse current of the pulsecurrents group.

FIG. 24 is a graph showing a slight short circuit transfer range andillustrating a form of the molten metal grain transfer against therelationship between a pulse duration TP and a pulse current IP when thewelding is carried out by switching periodically between the first pulsecurrents group and the second welding current under using aluminum wireof 1.2 mm diameter.

FIG. 25 is a graph showing a slight short circuit transfer range andillustrating a form of the molten metal grain transfer against therelationship between a pulse duration TP and a pulse current IP when thewelding is carried out by switching periodically between the first pulsecurrents group and the second welding current under using aluminum wireof 1.6 mm diameter.

FIG. 26 is a graph showing the relationship between the average value ofthe welding current Ia and the maximum value of the arc length variationLe in connection with a welding method based on a plurality of pulses toone molten metal grain transfer shown by a solid line CC and a weldingmethod based on one pulse to one molten metal grain transfer shown by adotted line.

FIG. 27 is a block diagram of a welding apparatus effecting a pulse MAGarc welding method of a preferred embodiment according to the presentinvention.

FIG. 28 is a graph illustrating a form of the molten metal graintransfer against the relationship between a pulse duration TP and apulse current IP when the welding is carried out by switchingperiodically between the first pulse currents group and the secondwelding current under using a soft steel wire of 1.2 mm diameter.

FIG. 29 is a graph illustrating a form of the molten metal graintransfer against the relationship between a pulse duration TP and apulse current IP when the MIG welding is carried out by switchingperiodically between the first pulse currents group and the secondwelding current under using a stainless steel wire of 1.2 mm diameter.

FIG. 30 (A) is a structural model view showing a time passage ofphenomenon to separate the molten metal grain form the terminal of wirewhen the first pulse currents group carries out a plurality of pulses toone molten metal grain transfer; FIG. 30 (B) is a graph showing the timepassage of the energized pulse current of the pulse currents group.

FIG. 31 is a graph illustrating the relationship between a pulseduration TP and a pulse current IP when the MIG welding is carried outby switching periodically between a plurality of pulses to one pulsemolten metal grain transfer range of the first pulse currents group andone pulse to one molten metal grain transfer range of the second pulsecurrents group under using an aluminum wire of 1.2 mm diameter.

FIG. 32 is a graph illustrating the relationship between a pulseduration TP and a pulse current IP when the MIG welding is carried outby switching periodically between a plurality of pulses to one pulsemolten metal grain transfer range of the first pulse currents group andone pulse to one molten metal grain transfer range of the second pulsecurrents group under using an aluminum wire of 1.6 mm diameter.

FIG. 33 is a graph illustrating the relationship between a pulseduration TP and a pulse current IP when the MIG welding is carried outby switching periodically between a plurality of pulses to one pulsemolten metal grain transfer range of the first pulse currents group andone pulse to a plurality of molten metal grains transfer range of thesecond pulse currents group under using an aluminum wire of 1.2 mmdiameter.

FIG. 34 is a graph illustrating the relationship between a pulseduration TP and the maximum value of the arc length variation Le inconnection with a welding method for switching periodically between aplurality of pulses to one pulse molten metal grain transfer range ofthe first pulse currents group and one pulse to a plurality of moltenmetal grains transfer range of the second pulse currents group underusing an aluminum wire of 1.6 mm diameter.

FIG. 35 is a graph showing the relationship between the average value ofthe welding current Ia and the maximum value of the arc length variationLe in connection with a welding method (a solid line C) for switchingbetween a plurality of pulses to one molten metal grain transfer rangeand one pulse to a plurality of molten metal grains transfer range and awelding method (a dotted line Z) based on the one pulse to one moltenmetal grain transfer range, wherein each of methods uses an aluminumwire of 1.2 mm diameter.

FIG. 36 is a graph showing the relationship between the average value ofthe welding current Ia and the maximum value of the arc length variationLe in connection with a welding method (a solid line C) for switchingbetween a plurality of pulses to one molten metal grain transfer rangeand one pulse to a plurality of molten metal grains transfer range and awelding method (a dotted line Z) based on the one pulse to one moltenmetal grain transfer range, wherein each of methods uses a stainlesssteel wire of 1.2 mm diameter

FIG. 37 is a graph illustrating the relationship between a pulseduration TP and a pulse current IP when the MIG welding is carried outby switching periodically between a plurality of pulses to one pulsemolten metal grain transfer range of the first pulse currents group andone pulse to a plurality of molten metal grains transfer range of thesecond pluse currents group under using an aluminum wire of 1.2 mmdiameter.

FIG. 38 is a graph illustrating the relationship between a pulseduration TP and a pulse current IP when the MIG welding is carried outby switching periodically between a plurality of pulses to one pulsemolten metal grain transfer range of the first pulse currents group andone pulse to a plurality of molten metal grains transfer range of thesecond pulse currents group under using an aluminum wire of 1.6 mmdiameter.

FIG. 39 is a graph showing the experimental result on the relationshipbetween a welding current I and an arc voltage V when the welding iscarried out by managing the pulse condition to change the arc length Ltinto Left and right at a constant wire feed rate.

FIG. 40 is a graph showing the relationship between the average value ofthe welding current Ia and the maximum value of the arc length variationLe in connection with a welding method (a solid line B) for switchingbetween one pulse to one molten metal grain transfer range and one pulseto a plurality of molten metal grains transfer range and a weldingmethod (a dotted line Z) based on the one pulse to one molten metalgrain transfer range.

FIG. 41 is a graph showing the relationship between a welding currentand an arc voltage when a MAG arc welding is carried out at apredetermined wire feed rate and illustrating a welding method of apreferred embodiment according to the present invention.

FIG. 42 is a table for determining in advance each of first arc voltagesetting values Un corresponding to each of wire feed rate setting valuesWn when a consumable electrode is fed at predetermined wire feed rate inaccordance with a MAG welding method and for determining in advance eachof second arc voltage setting values Vn corresponding to each of firstarc voltage setting values Un.

FIG. 43 is a table for determining in advance each of first arc voltagesetting values Un corresponding to each of first wire feed rate settingvalues when the consumable electrode is fed at a rate obtained byswitching periodically between the first wire feed rate and the secondwire feed rate in accordance with a MAG arc welding method, and fordetermining in advance each of second arc voltage setting values Vncorresponding to each of first arc voltage setting values Un inaccordance with each of second wire feed rate setting values Xn.

FIG. 44 is a graph showing a relationship between a switching frequencyF (horizontal axis) necessary for producing the vibration at the moltenpool and an arc length variation Le (vertical axis) between the firstarc length Lt and the second arc length Left and right when an aluminumplate AL is welded by a MIG welding method.

FIG. 45 is a graph showing a sectional view of bead obtained by changingthe average value of welding current Ia (horizontal axis) and theaverage value of an arc voltage Va (vertical axis) and showing also thearc length.

FIG. 46 is a graph showing a forming condition of the scale beadobtained with the variation in the average value of welding current Ia(a horizontal axis) and the arc length variation value Le (a verticalaxis).

FIG. 47 is a perspective view showing a pitch and a scale bead obtainedwith the MIG arc welding method to change the arc length according tothe present invention.

FIG. 48 is a graph showing the sectional view and the arc length of abead obtained with the variation in the average value of welding currentIa and the average value of arc voltages Va in a pulse MIG arc weldingmethod applied for a copper plate.

FIG. 49 is a graph showing the sectional view and the arc length of abead obtained with the variation in the average value of welding currentIa and the average value of arc voltages Va in a pulse MIG arc weldingmethod applied for a stainless steel plate.

FIG. 50 is a graph showing an effect of the embodiment carried out atthe butt joint by the welding method of a preferred embodiment accordingto the present invention and showing also a comparison between themethods according to the present invention and to the prior art.

FIG. 51 is a graph showing a time passage of a pulse current used in thebutt joint welding shown in FIG. 50.

FIG. 52 is a graph showing an effect of the embodiment carried out atthe gap of lap joint by the welding method of a preferred embodimentaccording to the present invention and showing also a comparison betweenthe methods according to the present invention and to the prior art.

FIG. 53 is a perspective view of a gap of lap join used in the weldingshown in FIG. 52.

FIGS. 54 (A), (B) and (C) are structural model views illustrating aphenomenon occurring with the increase in the gap of butt joint treatedwith the butt welding method and FIGS. 54 (D) and (E) are graphs showingthe time passage of the pulse current corresponding to the gaps of buttjoints shown in FIGS. (A) and (B).

FIGS. 55 (A) to (D) are structural model views for illustrating thephenomenon occurring with the decrease in the gap of butt joint in thebutt welding method of a preferred embodiment according to the presentinvention.

FIGS. 56 (A), (B) and (C) are structural model views illustrating aphenomenon occurring with the increase in the gap of lap joint treatedwith the lap welding method of a preferred embodiment of the presentinvention and FIGS. 54 (D) and (E) are graphs showing the time passageof the pulse current corresponding to the gaps of lap joints shown inFIGS. (A) and (B).

FIGS. 57 (A) to (D) are structural model views for illustrating thephenomenon occurring with the decrease in the gap of lap joint in thelap welding method of a preferred embodiment of the present invention.

FIG. 58 (A) is a structural model view illustrating the effect of thecorrection in the arc length carried out by the welding of a preferredembodiment of the present invention method when the gap of butt joint isincreased and FIG. 58 (B) is a structural model view illustrating theeffect of the correction of the arc length when the gap of butt joint isdecreased.

FIG. 59 (A) is a structural model view illustrating the effect of thecorrection in the arc length carried out by the welding method when thegap of lap joint is increased and FIG. 58 (B) is a structural model viewillustrating the effect of the correction of the arc length of apreferred embodiment of the present invention when the gap of lap jointis decreased.

FIG. 60 illustrates sectional views of welding beads obtained at a, b, cand d points on the solid line of FIG. 50 when the welding method shownin FIG. 50 is carried out at a constant wire feed rate and at theswitched wire feed rate, respectively.

FIG. 61 illustrates sectional views of welding beads obtained at a, b, cand d points on the solid line of FIG. 52 when the welding method shownin FIG. 52 is carried out at a constant wire feed rate and at theswitched wire feed rate, respectively.

FIG. 62 is a graph showing the relationship between a switchingfrequency and a cracking ratio in connection with a welding method of apreferred embodiment of the present invention.

FIG. 63 is a graph showing the relationship between the switchingfrequency F and the average crystal grain size SD in connection with awelding method of a preferred embodiment of the present invention.

FIG. 64 illustrates the effect on the cracking in connection with awelding method according to prior art and the welding methodcharacterized by fine grain size of a preferred embodiment according tothe present invention.

FIG. 65 is a graph showing the relationship between the arc lengthvariation value Le and the amplitude PW of the vibration of the moltenpool.

FIG. 66 is a graph showing the relationship between the arc lengthvariation value Le and the average crystal grain size SD in connectionwith a welding method of a preferred embodiment of the presentinvention.

FIG. 67 is a graph showing the relationship between the switchingfrequency F and the arc length variation value Le in connection with awelding method of a preferred embodiment of the present invention.

FIG. 68 (A) is a perspective view of the weld bead obtained with thewelding method of a preferred embodiment of the present invention; FIG.68 (B) is a graph showing the time passage of the amplitude of vibrationof the molten pool under welding in a melt proceeding direction; andFIG. 68 (C) is a structural model view showing the convection of thewelding metal in the molten pool.

FIG. 69 (A) and (B) indicate the radiation transmitting test results onthe materials by a conventional MIG welding method and a welding methodof a preferred embodiment of the present invention.

FIG. 70 (A) and (B) indicate waveforms of echo of the ultrasonic defectfinding test carried out on materials by a conventional MIG weldingmethod and the welding method of a preferred embodiment of the presentinvention.

FIG. 71 is a graph showing the relationship between an average crystalgrain size SD and a height of the echo in connection with the weldingmethod of a preferred embodiment of the present invention.

FIG. 72 is a graph showing the relationship between a switchingfrequency F and an average crystal grain size SD in connection with thewelding method of a preferred embodiment of the present invention.

FIG. 73 is a graph showing the relationship between an arc lengthvariation value Le and an amplitude PW of the vibration of the moltenpool in connection with the welding method of a preferred embodiment ofthe present invention.

FIG. 74 is a graph showing the relationship between an arc lengthvariation value Le and an average crystal grain size SD in connectionwith the welding method of a preferred embodiment of the presentinvention.

FIG. 75 is a graph showing the relationship between a switchingfrequency F and an arc length variation value Le in connection with thewelding method of a preferred embodiment of the present invention.

FIG. 76 is a graph showing the relationship between an arc voltagevariation value ΔVa and an arc length variation value Le in connectionwith the welding method without using the pulse.

FIG. 77 is a graph showing the relationship between a switchingfrequency F and an average crystal grain size SD in connection with thewelding method without using the pulse.

FIG. 78 is a graph showing the relationship between an amplitude PW ofthe vibration of the molten pool and the number of pores BN per 50 mm ofwelding length in connection with the welding method without using thepulse.

FIG. 79 is a graph showing the relationship between a switchingfrequency F and an amplitude PW of the vibration of the molten pool inconnection with the welding method of a preferred embodiment of thepresent invention.

FIG. 80 is a graph showing the relationship between a switchingfrequency F and the number of pores BN per 50 mm of welding length inconnection with the welding method of a preferred embodiment of thepresent invention.

FIG. 81 is a graph showing the relationship between an arc lengthvariation value Le and the number of pores BN per 10 cm of weldinglength in connection with the welding method of a preferred embodimentof the present invention.

FIG. 82 is a graph showing the relationship between an arc lengthvariation value Le and a switching frequency F in order to generate theamplitude PW of the molten pool in a size more than 0.5 mm in connectionwith the welding method of a preferred embodiment of the presentinvention.

FIG. 83 is a block diagram of the first embodiment of the weldingapparatus wherein the arc voltage is controlled by pulse frequency.

FIG. 84 is a block diagram of the second embodiment of the weldingapparatus wherein the arc voltage is controlled by pulse frequency.

FIG. 85 is a block diagram of the third embodiment of the weldingapparatus wherein the arc voltage is controlled by pulse frequency.

FIG. 86 is a block diagram of the fourth embodiment of the weldingapparatus wherein the arc voltage is controlled by pulse frequency.

FIG. 87 is a block diagram of the fifth embodiment of the weldingapparatus wherein the arc voltage is controlled by pulse frequency.

FIG. 88 is a block diagram of an embodiment of the welding apparatus forproducing the welding current waveform shown in FIG. 97.

FIG. 89 is a block diagram of an embodiment of the welding apparatus forproducing the welding current waveform shown in FIG. 96.

FIG. 90 is a block diagram of a circuit of a pulse frequency controlsignal generator shown in the block diagrams of FIGS. 83 to 89.

FIGS. 91(A)-91(F) are graphs showing the time passage of the outputsignal in the block diagram shown in FIG. 90.

FIG. 92 shows a waveform of the output current of the welding apparatusshown in the block diagram of FIG. 83.

FIG. 93 shows a waveform of the output current of the welding apparatusshown in the block diagram of FIG. 84.

FIG. 94 shows a waveform of the output current of the welding apparatusshown in the block diagram of FIG. 85.

FIG. 95 shows a waveform of the output current of the welding apparatusshown in the block diagram of FIG. 86.

FIG. 96 shows a waveform of the output current of the weldingapparatuses shown in the block diagrams of FIG. 87 to FIG. 89.

FIG. 97 shows a waveform of the output current of the welding apparatusshown in the block diagram of FIG. 88.

FIG. 98 is a block diagram of an embodiment of the welding apparatuswherein the arc voltage is controlled by pulse duration.

FIG. 99 is a block diagram of an embodiment of the welding apparatus forproducing the welding current waveform shown in FIG. 103.

FIG. 100 is a block diagram of an embodiment of the welding apparatusfor producing the welding current waveform shown in FIG. 102.

FIGS. 101(A)-101(E) are graphs showing the time passage of the pulseduration control signal shown in the block diagrams of the embodimentsof FIGS. 98 to 100.

FIG. 102 shows a waveform of the output current of the welding apparatusshown in the block diagram of FIGS. 98 and 100.

FIG. 103 shows a waveform of the output current of the welding apparatusshown in the block diagram of FIG. 99.

FIG. 104 is a block diagram of an embodiment of the welding apparatuswherein the arc voltage is controlled by base current value.

FIG. 105 is a block diagram of an embodiment of the welding apparatusfor producing the welding current waveform shown in FIG. 108.

FIG. 106 is a block diagram of an embodiment of the welding apparatusfor producing the welding current waveform shown in FIG. 107.

FIG. 107 shows a waveform of the output current of the welding apparatusshown in the block diagram of the embodiments in FIG. 104 and FIG. 106.

FIG. 108 shows a waveform of the output current of the welding apparatusshown in the block diagram in FIG. 105.

FIG. 109 is a block diagram of an embodiment of the welding apparatuswherein the arc voltage is controlled by pulse current value.

FIG. 110 is a block diagram of an embodiment of the welding apparatusfor producing the welding current waveform shown in FIG. 113.

FIG. 111 is a block diagram of an embodiment of the welding apparatusfor producing the welding current waveform shown in FIG. 112.

FIG. 112 shows a waveform of the output current of the welding apparatusshown in the block diagram in FIGS. 109 and 111.

FIG. 113 shows a waveform of the output current of the welding apparatusshown in the block diagram in FIG. 110.

DESCRIPTION OF THE SYMBOLS

1 . . . consumable electrode (wire)

1a, 1b . . . terminal of the wire

2 . . . welding material

3 . . . arc

4 . . . electric supplying tip

4a . . . terminal of electric supplying tip

L11, L21 . . . actual arc length

Ln, Lm . . . wire projection length

Lt, Left and right . . . apparent first and second arc lengths

Le . . . variation value of wire projection length (apparent) arc lengthvariation value

L1, L2 . . . arc characteristic of arc length L1, and L2

1PnD . . . one pulse to a plurality of molten metal grains transferrange

1P1D . . . one pulse to one molten metal grain transfer range

nP1D . . . plurality of pulses to one molten metal grain range

P1, P1, . . . P1 . . . first pulse currents group

P2, P2, . . . P2 . . . second pulse currents group

IP . . . pulse current (value)

IP1 . . . first pulse current value

IP2 . . . second pulse current value

IP3 . . . pulse current value

Ip31, IP32 . . . first and second pulse current value

TP . . . pulse duration

TP1 first pulse duration

TP2 . . . second pulse duration

Tp3 . . . pulse duration

TP31, TP32 . . . first and second pulse duration

f . . . pulse frequency

f1, f2 . . . first and second pulse frequency

f3 . . . pulse frequency

f31, f32 . . . first and second pulse frequency

Ib . . . base current (value)

Ib1 . . . first base current

IB2 . . . second base current

IB3 . . . base current

IB31, IN32 . . . first and second base current value

f . . . switching frequency

WS . . . welding speed

WF, WF1, WF2, WF3 . . . wire feed rate

Wf . . . wire feed rate setting value

D1 . . . (first) pulse period

D2 . . . second pulse period

I1 . . . first welding current value

I2 . . . second welding current value

T1 . . . first welding current energizing time (first pulse energizingperiod)

T2 . . . second welding current energizing time (second pulse energizingperiod)

Ds . . . energizing ratio

M1 . . . average value of welding current during

first pulse energizing period

M2 . . . average value of welding current during second pulse energizingperiod

I . . . welding current (value)

Ia . . . average value of welding current

ΔIa . . . variation value of welding current

V . . . arc voltage

Va . . . average value of arc voltage

Va1 . . . first arc voltage value

Va2 . . . second arc voltage value

ΔVa . . . variation value of arc voltage

WM . . . wire feeding motor

WC . . . wire feed rate control circuit

WD . . . wire feed rate detection circuit

Im . . . average current setting circuit (wire feed rate settingcircuit)

Im1 . . . first welding current setting circuit (first wire feed ratesetting circuit)

Im2 . . . second welding current setting circuit (second wire feed ratesetting circuit)

vs1 . . . (first) arc voltage setting circuit

VS2 . . . second arc voltage setting circuit

VD . . . arc voltage detection circuit

ID . . . welding current detection circuit

CM1 . . . wire feed rate comparing circuit (first comparator)

CM2 . . . (second) comparator

CM6 . . . welding current comparator

IP1 . . . (first) pulse current value setting circuit

IP2 . . . second pulse current value setting circuit

TP1 . . . (first) pulse duration setting circuit

TP2 . . . second pulse duration setting circuit

FP1 . . . (first) pulse frequency setting circuit

FP2 . . . second pulse frequency setting circuit

IB1 . . . (first) base current setting circuit

IB2 . . . second base current setting circuit

IB3 . . . base current controlling circuit

IP3 . . . pulse current value controlling circuit

SW1 . . . pulse current value switching circuit

SW2 . . . pulse duration switching circuit

SW3 . . . base current switching circuit

SW4 . . . pulse frequency switching circuit

SW5 . . . pulse base current switching circuit

SW6 . . . arc voltage switching circuit

SW7 . . . wire feed rate switching circuit (welding current switchingcircuit)

SW8 . . . constant current switching circuit

SW9 . . . short circuit current switching circuit

SW10 . . . pulse constant current switching circuit

PS . . . welding electric source controlling circuit

VF . . . pulse frequency signal generating circuit

VF3 . . . pulse frequency control signal generating circuit

DF . . . pulse duration frequency signal generating circuit

DF3 . . . pulse duration and frequency controlling signal generatingcircuit

HL . . . switching signal generating circuit

DT . . . energizing ratio setting circuit

FT . . . energizing frequency setting circuit

IS1 . . . first constant current setting circuit

IS2 . . . second constant current setting circuit

IT . . . short circuit current setting circuit

SD . . . short circuit detection circuit

WS . . . welding speed setting circuit

Wc . . . wire feed rate controlling circuit

Wd . . . feed rate detection circuit

Im . . . average current setting signal (wire feed rate setting signal)

Im1 . . . first welding current setting signal (first wire feed ratesetting signal)

Im2 . . . second welding current setting signal (second wire feed ratesetting signal)

Vs1 . . . (first) arc voltage setting signal

Vs2 . . . second arc voltage setting signal

Vd . . . arc voltage detection signal

Id . . . welding current detection signal

Cm1 . . . wire feed rate controlling signal

Cm2 . . . arc voltage controlling signal

Cm6 . . . welding current controlling signal

Vf . . . pulse frequency signal

Vf1, Vf2 . . . first and second pulse frequency signal

Vf3 . . . pulse frequency controlling signal

Vf31, Vf32 . . . first and second pulse frequency controlling signal

H1 . . . switching signal

Ip . . . pulse current value setting signal

Ip1, Ip2 . . . first and second pulse current value setting signal

Ip3 . . . pulse current controlling signal

Ip31, Ip32 . . . first and second pulse current controlling signal

Tp . . . pulse duration setting signal

Tp1, Tp2 . . . first and second pulse duration setting signal

Tp3 . . . pulse duration controlling signal

Tp31, Tp32 . . . first and second pulse duration setting signal

Fp . . . pulse frequency setting signal

Fp1, Fp2 . . . first and second pulse frequency setting signal

Ib . . . base current setting signal

Ib1, Ib2 . . . first and second base current setting signal

Ib3 . . . base current controlling signal

Ib31, Ib32 . . . first and second base current controlling signal

S1 . . . switching pulse current signal

S2 . . . switching pulse duration signal

S3 . . . switching base current signal

S4 . . . switching pulse frequency signal

S5 . . . switching pulse base current signal

S6 . . . switching arc voltage signal

S7 . . . switching wire feed rate signal

S8 . . . switching constant current signal

S9 . . . short circuit switching signal

S10 . . . pulse constant current switching signal

Df . . . pulse duration frequency signal

Df1, Df2 . . . first and second pulse duration frequency signal

Df3 . . . pulse duration frequency controlling signal

Df31, Df32 . . . first and second pulse duration frequency controllingsignal

Dt . . . energizing ratio signal

Pf . . . pulse controlling signal

Pf1, Pf2 . . . first and second pulse controlling signal

It . . . short circuit current setting signal

Sd . . . short circuit detection signal

BEST MODE FOR EMBODYING THE INVENTION

Embodiment 1, Description of FIG. 13 FIG. 13 shows various ranges forvarious forms of molten metal grains transfer on a graph having a pulseenergizing time TP ms (referred to pulse duration) plotted at ahorizontal axis and a pulse current IP A plotted at a vertical axis whenan aluminum plate is welded with aluminum wire of 1.2 mm diameter at anaverage welding current Ia=100 A, and a base current Ib=30 A with apulse MIG arc welding method. In FIG. 13, a range BB is a spray transferrange for a long arc length, while a range DD is a short circuittransfer range at which the arc disappears. At a range CC, an arc lengthis an intermediate length between a length at the spray transfer rangeBB and a length at the short circuit transfer range DD. The range CC hasa slight short circuit generated therein. The molten metal transfer iscarried out by the spray transfer. The range CC is a so called mesospray transfer range. Among the above spray transfer range BB, a rangeshown by a oblique line is a one pulse to one molten metal grain rangewhere the pulse current and the molten metal transfer are synchronizedto each other. Further, this range is divided into a BBA range at whichthe arc length is more than 6 mm, a BBB range at which the arc length is4 to 6 mm and BBC range at which the arc length is 2 to 4 mm.

Embodiment 2, Description of FIG. 14

FIG. 14 (A) shows a relationship between an average value Ia A of thewelding currents (horizontal axis) and an average value Va V of arcvoltages (vertical axis) when aluminum alloy plate is welded with analuminum alloy consumable electrode of 6 mm diameter through a MIG arcwelding method. In FIG. 14 (A), a wire feed rate WF1 to WF3 ispredetermined at a given value, and the distance between the terminal 4aof electricity supplying tip and the surface of the welding material 2ais changed mechanically. The measurement is carried out with therelationship among the average value Ia A of welding current, theaverage value Va V of the arc voltages and arc length L mm shown in FIG.14 (B). A range AA lower in the current than the critical current IC isa drop transfer range, and a range BB higher in the current than thecritical current Ic is a spray transfer range. A range CC shown by aoblique line is a range having an intrinsic self-regulation effect ofarc length, that is, a so called meso spray transfer range, and a rangeDD below the oblique line is a short circuit transfer range.

In a meso spray transfer range CC of FIG. 14 (A), the average value Iaof the welding currents decreases with a decrease in the arc length L atthe constant value of the wire feed rate WF as described above. This isequivalent to a fact that the wire feeding amount, that is, the meltingspeed of the wire fed increases with a decrease in the arc length at aconstant value of the welding current. As a result, the arc length iscontrolled automatically in a way that the arc length increases with anincrease in the wire melting amount resulting from the lowering of thearc voltage. This is an intrinsic self-regulation effect of arc length.This regulation can be seen with the welding of an aluminum plate.

In the meso spray transfer range CC in FIG. 14 (A), a white circle and adotted line indicate a case in which the first pulse currents group arecontrolled to be in one pulse to one molten grain mode, and a blackcircle and a solid line indicate the meso spray mode in which the firstpulse currents group or the first welding current value without pulse isset to be a value to generate a slight short circuit. In a range havingthe arc length of 2 to 9 mm of the meso spray transfer range in FIG. 14(A), the meso spray mode shown by a solid line is larger in thecurvature than the one pulse to one molten metal grain mode shown by adotted line. Accordingly, the first pulse current group or the firstwelding current set to the meso spray mode causes a large variation inthe wire melting amount at the wire feed rate and the welding currentthe same as that of other case. As a result, it is possible to make theslight short circuit time shorter, the slight short circuit number lessand then the arc length shorter.

In view of the above reason, the one pulse to one molten metal grainmode is set up at the spray transfer range BB while the meso spray modeto generate the slight short circuit is set up at the meso spraytransfer range CC. A periodical switching method between both modesrepeats alternatively the enlargement of the molten pool due to theexpansion of the arc and the fulfilling of the molten metal due to theconvergence of the arc. As a result, the control of the molten metal hasa larger effect than the control at the spray transfer range BB not toproduce the short circuit. It is noted that the first pulse currentsgroup or the first welding current causes the slight short circuit togenerate 2 to 8 times per sec and then the short circuit transfer is notcarried out because tile short circuit time is less than 1.5 msec perone time according to the welding method of the present invention. Theconventional short arc welding method has the short circuit generated 20to 100 times per sec and has a long short circuit more than 2 msec perone time. There is accordingly a clear difference in the slight shortcircuit between the welding method according to the present inventionand the welding method according to the prior art. The welding methodaccording to the present invention differs clearly from the conventionalwelding method to repeat periodically the spray transfer and the shortcircuit transfer and can obtain the scale bead in a regular ripplepattern in a similar way to that of the TIG filler arc welding method.

With reference to FIGS. 15 and 16, the description will be directed tothe relationship among the average value Ia A of the welding currents orthe variation value ΔIa A, the variation value ΔVa V of the arc voltagesand the variation value Le mm of the arc Length.

Embodiment 3, Description of FIG. 15

FIG. 15 relates to the embodiment of the basic welding method accordingto the present invention and is a graph showing the relationship betweenthe variation value ΔVa V of the arc voltages (horizontal axis) and thevariation value Le mm of the arc length (vertical axis) with a constantsetting value of the wire feed rate. The welding conditions of FIG. 15are as follows: electrode, aluminum wire 5183 of 1.2 mm diameter; pulsecurrent value IP, 280 A; pulse duration TP, 1.2 ms; average value of thewelding current Ia, 100 A as shown by a curve 100; average value of thearc voltage Va, 19 V; or average value of the welding current Ia, 200 Aas shown by a curve 200; average value of arc voltage Va, 20 V. Withreference to FIG. 15, the description will be directed to a case whenthe set average value of welding current Ia changes from 100 A to 200 A.In order to obtain the variation value of the arc length Le of 6 mm thesame as each other, the variation value of the arc voltage is ΔVA=1.5 Vas shown by a point Q1 on the curve A100 at the case of Ia=100 A whereasthe variation value of the arc voltage is ΔVa=2.0 V as shown by a pointQ2 on the curve A200 at the case of La=200 A. It is clear that thelatter case has the variation value of the arc voltage higher than thatof the former case. That is, an increase in the average value of thewelding currents Ia requires an increase in the variation value of thearc voltages ΔVa in order to obtain the variation value of the arclength the same as each other.

Embodiment 4, Description of FIG. 16

FIG. 16 is a graph showing the variation value of the arc length Leobtained with a case when the welding is carried out at a larger weldingcurrent by changing largely the conventional wire feed rate and the Leobtained by changing the welding current value and the arc voltage valuein the additional welding method according to the present invention asmentioned above. The welding conditions in FIG. 16 are carried out byusing an aluminum wire A5183 at the average value of the welding currentIa=90 A and the arc voltage Va=19 V. The graph shown in FIG. 16 has thevariation value of the welding current ΔIa A plotted at a horizontalaxis and the variation value of the arc voltages ΔVa V plotted at avertical axis. The curves Le=1, Le Feibush and Le=6 can be obtained byplotting the measuring points corresponding to the variation value Le ofthe arc length of 1, 3 and 6 mm, respectively. With reference to FIG.16, the case ΔIa=0 is the same case as that when the average value ofthe welding currents Ia is made constant without changing the wire feedrate according to the basic welding method of the present invention. Inorder to obtain Le=1, Le Feibush and Le=6 mm, the variation value of thearc voltage must be 0.3, 1.1 and 2.0 V.

On the horizontal axis of FIG. 16, ΔIa=50 A is corresponding to a casewhen the welding is carried out by switching the conventional wire feedrate to change largely the variation value of the welding current ΔIa.As shown by points Q51, Q53 and Q56, in order to obtain the variationvalue of the arc length Le=1, Le Feibush and Le=6 mm, it is necessary tosatisfy the following relation; the variation value of the arc voltageΔVa=1, 3.1 and 6 V, respectively.

In the additional welding method according to the present invention,when the variation value ΔIa is determined to be 15 A which is within arange of 10 to 15% of the average value of the welding current, forexample, 100 A, the variation value of the arc length Le=1, Le Feibushand Le=6 mm can be obtained by determining the variation value of thearc voltage in the following way; ΔVa=0.3, ΔVa=1.5 and ΔVa=2.5 V,respectively which are lower than those of the conventional weldingmethod.

In the conventional welding method changing largely the welding current,a large variation in the arc length requires a large variation in thevariation value of the arc voltage ΔVa. In order to achieve therequirement, it is necessary to change largely one or more than twoamong the pulse current, pulse duration, pulse frequency and basecurrent of the second pulse currents group in response to the pulsecurrent value, pulse duration, pulse frequency and the base currentvalue of the first pulse currents group. However, the base current in atoo much large size prevents the molten transfer from synchronizing withthe pulse. On the other hand, the pulse current value in a too muchlarge size causes the arc force to be too much strong and thepenetration depth to be large and then results in the melt down.Accordingly, it has not been possible for the conventional weldingmethod having the welding current changed largely to change the arclength largely.

With reference to FIGS. 17 and 18, the following description will bedirected to the relationship among the average value of the weldingcurrent Ia, the variation value of the average welding current ΔIa A,the variation value of the arc voltage ΔVa V, and the variation value ofthe arc length Le mm.

Embodiment 5, Description of FIG. 17

FIG. 17 is a graph showing the relationship between the variation valueof the arc voltage ΔVa V and the variation value of the arc length Le mmwhen the basic welding method according to the present invention iscarried out in a way for managing the wire feed rate to have the averagevalue of the welding current Ia held at a constant value. The weldingcondition of FIG. 17 is as follows: electrode=stainless steel SUS308 ina diameter 1.2 mm; pulse current value IP=380 A; pulse duration TP=1.2ms; average value of welding current Ia=100 A and arc voltage Va=20 V asshown by a curve S 100 or average value of welding current Ia=200 A andaverage value of arc voltage Va=22 V as shown by a curve S 200. Withreference to FIG. 17, the description will be directed to a case whenthe set average value of welding current Ia changes from 100 A to 200 A.In order to obtain the variation value of the arc length Le of 6 mm thesame as each other, the variation value of the arc voltage is ΔVA=3.0 Vas shown by a point Q3 on the curve S100 at the case of Ia=100 A whereasthe variation value of the arc voltage is ΔVa=3.5 V as shown by a pointQ4 on the curve S200 at the case of La=200 A. It is clear that thelatter case has the variation value of the arc voltage higher than thatof the former case. That is, an increase in the average value of thewelding currents Ia requires an increase in the variation value of thearc voltages ΔVa in order to obtain the variation value of the arclength the same as each other.

Embodiment 6, Description of FIG. 18

FIG. 18 is a graph showing the variation value of the arc length Leobtained with a case when the welding is carried out at a larger weldingcurrent by changing largely the conventional wire feed rate and the Leobtained by changing the welding current value and the arc voltage valuein the additional welding method according to the present invention asmentioned above. The welding conditions in FIG. 18 are carried out byusing a stainless steel wire SUS 308 of diameter 1.2 mm at the averagevalue of the welding current Ia=90 A and the arc voltage Va=19 V. Thegraph shown in FIG. 18 has the variation value of the welding currentΔIa A plotted at a horizontal axis and the variation value of the arcvoltages ΔVa V plotted at a vertical axis. The curves Le=1, Le Feibushand Le=6 can be obtained by plotting the measuring points correspondingto the variation value Le of the arc length of 1, 3 and 6 mm,respectively.

With reference to FIG. 18, the case ΔIa=0 is the same case as that whenthe average value of the welding currents Ia is made constant withoutchanging the wire feed rate according to the basic welding method of thepresent invention. In order to obtain Le=1, Le `Feibush and Le=6 mm, thevariation value of the arc voltage ΔVa must be 0.7, 1.5 and 3.0 V.

On the horizontal axis of FIG. 18, ΔIa=50 A is corresponding to a casewhen the welding is carried out by switching the conventional wire feedrate to change largely the variation value of the welding current ΔIa.As shown by points Q61, Q63 and Q66, in order to obtain the variationvalue of the arc length Le=1, Le Feibush and Le=6 mm, it is necessary tosatisfy the following relation; the variation value of the arc voltage,ΔVa=2, 4 and 6 V, respectively.

In the additional welding method according to the present invention,when the variation value ΔIa is determined to be 20 A which is within arange of 10 to 20% of the average value of the welding current, forexample, 90 A, the variation value of the arc length Le=1, Le Feibushand Le=6 mm can be obtained by determining the variation value of thearc voltage in the following way; ΔVa=1.0, ΔVa=2.2 and ΔVa=4.0 V,respectively which are lower than those of the conventional weldingmethod.

The next description is the same as that of the embodiment 4 in FIG. 16and accordingly should be omitted.

Description of current switching

In FIG. 11, a switching signal shown in FIG. 11 (B) switches between thefirst pulse currents group and the second currents group with anenergizing ratio Ds=T2/(T1+T2) between the second pulse energizingperiod T2 and the first pulse energizing period T1. This switchingfrequency F=1/(Ti+T2) is set: to a suitable value, for example, 0.5 to25 Hz in order to achieve the aimed welding result. The pulse switchingfrequency is in a close relation to the welding speed and is preferablyselected in connection with the welding speed from the following table.

                  TABLE 1                                                         ______________________________________                                        welding speed  cm/min!                                                                        switching frequency  Hz!                                      ______________________________________                                        10-30           1.5                                                           30-50           3                                                             50-90           5                                                              90-120         8                                                             120-180         10                                                            180-300         15                                                            ______________________________________                                    

As shown in Table 1, the switching frequency is in a close relation tothe welding speed for obtaining a suitable welding result. Hence, it ispossible to switch between the first pulse energizing period and thesecond energizing period by generating a switching signal in a frequencycorresponding to that of the signal set to the welding speed.

In connection with the selection of the energizing ratio Ds, when thesecond pulse energizing period T2 is longer than the first energizingperiod, the arc length becomes larger and the sputter is easilygenerated. Therefore, it is desirable that the second pulse energizingperiod T2 is shorter than the first energizing period T1, and theenergizing ratio Ds=T2/(Ti+T2) is selected to be less than 0.5.

Further, when the variation value of the pulse current between the firstpulse current IP1 and the second pulse current IP2 is large, the sputteris easily generated with the switching of both currents at the sametime. It is desirable to switch at a plurality of times in order toachieve a gradual increase or decrease shown by a step form, a slopeform or the combination of the both.

Description of FIG. 19

FIG. 19 is a block diagram of the welding apparatus for carrying out theMIG arc welding at the meso spray transfer range at which the slightshort circuit generates as described with the FIG. 14.

In general, the welding at the meso spray transfer range can be carriedout by using a welding output control circuit having a constant currentcharacteristic. The wire feed rate is set in advance to a constant valueand the arc length is controlled to be in a constant value according tothe intrinsic self-regulation effect of arc length as mentioned above.When the short circuit generates, this welding method detects the shortcircuit and energizes the welding current higher than that of theordinal time to make the re-ignition of the arc.

In the welding apparatus according to this embodiment, the MIG arcwelding at this meso spray transfer range CC is carried out by using awelding output power having a constant current characteristic. Hence,there are two methods for switching periodically the arc length; one isto switch the setting value of the welding current, and ancther is toswitch the wire feed rate. Because the wire feed rage is changed at thesame time with the switching of the setting value of welding current,the present embodiment adapts a method to change the arc lengthperiodically by switching periodically the wire feed rate.

In FIG. 19, a first wire feed rate setting circuit WH and a second wirefeed rage setting circuit WL are circuits to set the arc lengths respectto the first and second welding conditions, and output a first wire feedrate setting signal Wh and a second wire feed rate setting signal Wi,respectively. A switching circuit H generates a switching signal H1 toswitch between the first welding condition and the second weldingcondition. A wire feed rate switching circuit SW7 generates a wire feedrate switching signal S7 by managing the switching Signal H1 to switchbetween a signal Wh and a signal Wi. A wire feed rate comparator circuitCM1 generates a wire feed rate control signal Cm1 obtained with thedifference between a signal S7 and a rate detection signal Wd. A firstconstant current setting circuit IS1 generates a first constant settingsignal Is1 for energizing the first constant current I1 at the small arclength. A second constant current setting circuit IS2 generates a secondconstant current setting signal Is2 for energizing a second constantcurrent I2 for the long arc length. A constant current switching circuitSW generates a constant current switching signal S8, and a short circuitcurrent setting circuit IT generates a short circuit setting signal Itfor energizing the welding current higher than that at the arcgeneration. A short circuit detection circuit SD generates a shortcircuit detection signal Sd when the short circuit is generated by aninput of arc voltage detection signal Vd generated from an arc voltagedetection circuit VD. A short circuit current switching circuit SW9generates a short circuit switching signal S9 by switching a switchingconstant current signal S8 to a short circuit current setting signal It.A welding current comparator circuit CM6 receives a welding currentdetection signal Id from a short circuit switching signal S9 and awelding current detection circuit ID and outputs a welding currentcontrol signal Cm6 corresponding to the difference between both signalsto a welding output control circuit PS no control the welding current.In such a case when an aluminum plate is welded by a MIG welding methodat the meso spray transfer range CC, the variation in the arc voltageincreases with the large variation in the arc length because the arcflies far away to the oxide film. Hence, it is difficult to control thearc length by detecting the arc voltage. Therefore, it is possible tocontrol the penetration shape by changing the arc length equivalent tothe shortest distance between the terminal 1a of consumable electrodeand the surface of molten pool of the welding material.

In FIG. 19, when the switching signal H1 switches between the firstconstant current setting circuit IS1 and the second constant currentsetting circuit IS2, the operation point mentioned before moves betweenpoints A and B. In FIG. 19, the first wire feed rate setting circuit WHand the second wire feed rat setting circuit WL are switched to eachother, the operation point mentioned before moves between points A andC, and the arc length changes from Lt to Left and right without changingthe welding current I1 with a variation in the arc voltage value from V1to V3.

Welding method

A pulse MAG arc welding method is characterized by the following steps:A first welding current of the pulse currents group is set to a value toform the spray transfer accompanied with a slight short circuit withholding the wire feed rate at a nearly constant value. The secondwelding current value without pulse is switched periodically within thespray transfer range at which a slight short circuit does not generate.As shown in FIG. 7, the wire extension length Ln or Lm between theterminal 4a of the electric supplier tip and the end terminal of wire 1aor 1b is periodically switched to each other while the arc length Leftand right or Lt of a shortest distance between the terminal 4a and thesurface of welding material 2 is periodically changed.

The pulse MAG arc welding method is a pulse MAG arc welding method toenergize the welding current obtained with the periodic switchingbetween the first welding current of the pulse current group and thesecond welding current without pulse and is characterized by thefollowing steps: First, the wire is fed at a constant rate determined inadvance. A pulse current value, pulse energizing time and a pulsefrequency as well as a base current value of each of the first weldingcurrent is set to a value to permit the material in a synchronizing waywith each of pulse currents accompanied slightly with a slight shortcircuit. The second welding current is energized within the spraytransfer range at which a slight short circuit does not generate. Thewelding is carried out by changing periodically the arc length inaccordance with the variation in the wire extension length between theterminal of the electric supplier tip and the end terminal of the wire.

Embodiment 7, Description of FIG. 20

The embodiment 7 is a case where an aluminum alloy plate A5052 inthickness of 6 mm is welded by using an aluminum alloy A5183 electrodeof 1.2 mm diameter with a pulse MIG arc welding method. FIG. 20 (A)shows an appearance of the bead obtained with the welding conditionsdescribed below. The bead has a regular ripple of pattern the same asthat obtained with TIG filler arc welding method as shown in FIG. 1.

A first welding current is a pulse current group having a constantcharacteristics and a second welding current is a direct current havinga constant current characteristic. The average value of the weldingcurrent is Ia=150 A.

first arc voltage Va1=19.5 V

(slight short circuit transfer mode, arc length Lt Feibush mm)

second arc voltage Va2=22.5 V

(spray mode, arc length Left and right=8 mm)

switching frequency F=2 Hz

welding speed WS=40 cm/min

pulse condition for slight short circuit spray transfer mode

pulse current value IP=320 A

pulse energizing time TP=1.2 ms

base current value IB=30 A

The penetration depth obtained with the same welding condition as theabove increases with a welding proceeding direction according to theprior art as shown in FIG. 20 (C), On the other hand, the penetrationdepth is of the repeat of a given value in a synchronizing way to theswitching frequency and is a stable depth as shown in FIG. 20 (B)according to the welding method of the present invention

Embodiment 8, Description of FIG. 21

FIG. 21 (A) is a graph showing a waveform to practice the welding methodaccording to claim 8. A first welding current comprises pulse currentgroup which has a short arc length in 2-4 mm and carries out the mesospray transfer accompanied occasionally with a slight short circuitduring the spray transfer. The average value of the welding current isexpressed by M1. The second welding current is a direct current to carryout the spray transfer without generation of the slight short circuithaving the arc length more than 6 mm. The average value is expressed byI2. FIG. 21 (B) is a graph showing a switching signal H1 for switchingbetween the first welding current and the second welding current.

Description of FIGS. 22 to 24

FIGS. 22 to 24 are graphs illustrating the welding method.

FIG. 22 (A) is a structural model view showing the time passage of thephenomenon in which the molten metal grain separates from the terminalof the wire when one pulse to one molten metal grain transfer mode isachieved. FIG. 22 (B) is a graph showing the time passage of the pulsecurrent. In FIG. 22 (B), a reference character P1 denotes each of thepulse currents; a reference character IP1, a pulse current value; areference character TP1, pulse duration; a reference character D1, pulsefrequency. The positions R1 to R5 of the time passage of each pulsecurrent P1 are corresponding to the various steps of melting at the wireterminal 1e, formation of molten bead 1c, separation of molten bead 1cfrom the wire terminal 1a and transportation of the molten metal grainto the welding material 2. In such a way, the one pulse to one moltenmetal grain mode 1P1D is carried out with each of pulses to execute themolten metal grain transfer.

Description of FIG. 23

FIG. 23 (A) is a structural model view showing the time passage of thephenomenon in which the molten metal grain separates form the wireterminal when a plurality of pulse to one molten metal grain transfermode is carried out. FIG. 23 (B) is a graph showing the time passage ofthe pulse current.

When the arc length is made shorter by decreasing the pulse current IPor pulse duration TP or both of them to a size smaller than the 1P1Drange mentioned above, at the time t3 shown in FIG. 23 (A), there isgenerated a state just after the separation of the molten bead 1d fromthe wire terminal 1a. The pulse at this time synchronizes with the pulseP11 at the first position of the first pulse group. After that, themolten metal grain is not transferred with the pulse currents P12 to P14at the second to the fourth positions. That is, in the first pulsecurrent group, there is generated a plurality of pulses to one moltenmetal grain mode in which one pulse current among a plurality of pulsecurrents synchronizes with the one molten metal transfer. The pluralityof pulses to one molten metal grain transfer range nP1D has no spattergenerated therein and is practically useful in the same way as the onepulse to one molten metal grain range 1P1D.

However, when the pulse current Ip or pulse energizing time TP or bothof them is made lower than the plurality of pulse to one molten metalgrain transfer range nP1D, the short circuit starts to generate and thepulse current does not synchronize with the molten metal transfer. Theshort circuit generates the spatter. Accordingly, the short circuittransfer range DRP is excluded from the range for which the presentinvention is applicable because the short circuit transfer range can notproduce a scale bead obtained with the TIG filler arc welding methodincluded in the aluminum MIG arc welding method which is one of theapplication of the present invention.

Description of FIGS. 24 and 25

FIG. 24 is a graph showing a molten metal grain transfer form as afunction of the pulse duration TP ms (horizontal axis) and the pulsecurrent IP A (vertical axis) when the welding method is carried out withan aluminum wire A5183 by using the pulse current in a welding currentaverage value Ia=100 A. Reference characters DRP, nP1D and 1P1D denotethe short circuit transfer range, a plurality of pulse to one moltenmetal grain transfer range and one pulse to one molten metal graintransfer range, respectively as mentioned with FIGS. 22 and 23. A symbolCC indicates a range which has the slight short circuit generatedtherein and comprises a total of the one pulse to plurality of moltenmetal grain transfer range, a lower part of the one pulse to pluralityof molten metal grain transfer range and a upper part of the shortcircuit transfer range and is nearly the same as the meso spray transferrange described in FIG. 14.

FIG. 25 is a graph showing a molten metal grain transfer form as afunction of the pulse duration TP ms (horizontal axis) and the pulsecurrent IP A (vertical axis) when the welding method is carried out withan aluminum wire A5183 by using the pulse current in a welding currentaverage value Ia=120 A. The next description will be the same as thedescription with FIG. 24 and accordingly, should be omitted.

Description of FIG. 26

FIG. 26 is a graph showing the relationship between then average valueof the arc welding current Ia A (horizontal axis) and the maximum valueof the variation value of the arc length Le mm, in connection with awelding method in a plurality of pulse to one molten metal graintransfer range having a slight short circuit shown by a solid line and awelding method in a one pulse to one molten metal grain transfer rangeshown by a dotted line in a case when an aluminum wire A5183 of adiameter 1.2 mm is used. With reference to FIG. 26, at the average valueof the welding current Ia=60 A, the welding method 1P1D shown by adotted line has the maximum value of the arc length variation value Le=2mm whereas the welding method shown by a solid line CC has the maximumvalue of the arc length variation value Le=4 mm which is two timeslarger than that of the 1P1D welding method. As a result, the weldingmethod shown by a solid line CC can expand the application field carriedout by the welding method 1P1D shown by a dotted line in connection withthe welding for the thin plate executed by a low current.

Embodiment 9, Description of FIG. 27

FIG. 27 is a block diagram of a welding apparatus of the embodimentpracticing the pulse MAG arc welding method. This block diagram has acontrolling circuit for energizing the pulse current formed thereininstead of the first constant current setting circuit IS1 and theconstant current switching circuit SW of FIG. 19. The description thesame as that of FIG. 19 therefore should be omitted. In FIG. 27, a pulsecurrent value setting circuit IP generates a pulse current value settingsignal while a base current setting circuit IB generates a base currentvalue setting signal Ib. A pulse duration setting circuit TP generates apulse duration setting signal Tp. A pulse frequency control signalgenerator circuit VF3 generates a pulse frequency control signal Vf3 inresponse to the arc voltage control signal Cm2. A pulse durationfrequency control signal generator circuit DF3 generates a pulseduration frequency control signal Df3 comprising a pulse durationsetting signal Tp and a pulse frequency control signal Vf3. A pulse basecurrent switching circuit SW5 generates, at the first welding current, apulse current setting signal Ip and a base current setting signal Ib aswell as a switching pulse base current signal S5 repeating at afrequency f determined by the first pulse duration frequency controlsignal Df3. Next, the second welding current, the pulse base currentswitching circuit SW5 generates a constant current setting signal Is2set by constant current setting circuit IS2. Further, a short circuitswitching circuit SW9 generates a short circuit switching signal S9 byswitching between a constant current setting signal Is2 and a shortcircuit current setting signal It, whereas a pulse constant currentswitching circuit 10 outputs a pulse constant current switching signalS10 to a welding output control circuit PS by switching between awelding current control signal Cm9 and a switching pulse base currentsignal S5.

The welding method is carried out in a way that a first welding currentfor obtaining the first arc length is a first pulse current group andthe second welding current for obtaining the second arc length energizesthe second pulse current group.

In welding methods, when the first pulse current group has a smallcurrent and a short arc length, the mode becomes a spray transfer modehaving a slight short circuit generated therein as described above.

In welding methods, when the first pulse current group has a relativelylarge pulse current value or a relatively long arc length, the mode isin a spray transfer mode having no slight short circuit.

The following description will be directed to a suitable range of apulse current IP and a pulse duration TP capable of energizing the firstpulse current group and the second pulse current group without causingthe short circuit transfer mode and a transfer form.

Embodiment 10, Description of FIG. 28

FIG. 28 is a graph showing that a range permitting the one pulse to onemolten metal grain transfer mode is within a range Δ1P1D shown by aoblique line in connection with a pulse duration TP ms (horizontal axis)and a pulse current IP A (vertical axis) when the pulse MAG arc weldingmethod is carried out at a welding current average value of 100 A at anarc length of 3 mm by using a soft steel wire of 1.2 mm diameter (JIS,YGW-12) and a sealed gas of a mixture of 80% of argon gas and 20% ofcarbon dioxide gas.

FIG. 29 is a graph showing that a range permitting the one pulse to onemolten metal grain transfer mode is within a range 1P1D shown by aoblique line in connection with a pulse duration TP ms (horizontal axis)and a pulse current IP A (vertical axis) when the pulse MAG arc weldingmethod is carried out at a welding current average value of 100 A at anarc length of 3 mm by using a stainless steel wire of 1.2 mm diameterand a sealed gas of a mixture of 98% of argon gas and 2% of oxygen gas.

As shown in FIGS. 28 and 29, the range shown by a oblique line isnarrow. It is difficult for the welding method in a one pulse to onemolten metal grain transfer mode to switch periodically a suitable pulsecurrent, pulse duration or the both of them.

The following description will be directed to a welding method capableof enlarging the applicable range which has less short transfer modegenerated therein than the range capable of generating the one pulse toone molten metal grain transfer mode is possible.

Description of FIG. 30

With reference to FIGS. 28 and 29, the arc length is made shorter bydecreasing the pulse current value IP, the pulse duration TP or the bothof them to a size smaller than the 1P1D one pulse to one molten metalgrain transfer range shown by a oblique line. Thus, at the time t3 shownin FIG. 30 (A), there is generated a state just after the separation ofthe molten bead 1d from the wire terminal 1a. The pulse at this timesynchronizes with the pulse P11 at the first position of the first pulsegroup. After that, the molten metal grain is not transferred with thepulse currents P12 to P14 at the second to the fourth positions. Thatis, in the first pulse current group, there is generated a plurality ofpulses to one molten metal grain mode in which one pulse current among aplurality of pulse currents synchronizes with the one molten metaltransfer. The plurality of pulses to one molten metal grain transferrange nP1D has no spatter generated therein and is practically useful inthe same way as the one pulse to one molten metal grain range 1P1D.

However, when the pulse current Ip or pulse energizing time TP or bothof them is made lower than the plurality of pulse to one molten metalgrain transfer range Δ nP1D, the short circuit starts to generate, andthe pulse current does not synchronize with the molten metal transfer.The short circuit at the short circuit transfer range DRP shown in FIGS.28 and 29 generates the spatter. Accordingly, the short circuit transferrange DRP is excluded from the range for which the present invention isapplicable because the short circuit transfer range can not produce ascale bead obtained with the TIG filler arc welding method included inthe aluminum MIG arc welding method which is one of the application ofthe present invention.

With reference to FIG. 28, the arc length is made longer by increasingthe pulse current value IP or the pulse duration TP to a size largerthan the 1P1D one pulse to one molten metal grain transfer range shownby a oblique line. Thus, at the time t8 and t9 shown in FIG. 30 (A),there is generated a state which causes, two times, the separation ofthe molten bead 1d from the wire terminal 1a. The pulse at this timesynchronizes with the pulse P21 at the first position of the first pulsegroup. After that, there occurs a case at which the molten metal grain1d separates two times with the pulse current P22 at the secondposition. That is, during a pulse period between a pulse current and thenext pulse current, a plurality of molten metal grains are transferred.At least one of the molten transfer is a one pulse to plurality ofmolten metal grains transfer range Δ1PnD which is synchronizing with thepulse current.

When the pulse current value and the pulse duration are made larger thanthose in this range,the molten metal extends into a string so that themolten metal transfer mode is changed to a so called streaming transfermode STR which is in no relation with the energizing of the pulsecurrent, that is, which does not synchronize with the pulse current.Within this range STR, the arc length can not follow the variation inthe wire extension length or wire feed rate, and produces a shortcircuit to generate spatter.

It is noted that a so called project transfer range is a range at whichthe molten metal transfer synchronizes with the energizing of the pulsescomprising those of three ranges of the one pulse to a plurality ofmolten metal grains range Δ1PnD, the one pulse to one molten metal grainrange 1P1D, and a plurality of pulses to one molten metal grain nP1D.Therefore, in the welding method the first pulse current group is set toa short range corresponding to the short arc length at the plurality ofpulses to one molten metal grain transfer range nP1D whereas the secondpulse current group is set to the long range corresponding to a long arclength at the one pulse to a plurality of molten metal grains Δ1PnD. Thewelding method can be said to be a method to switch between the both ofthe first and second pulse current groups. Further, the welding methodis aimed to be applicable for the ranges of a plurality of pulse to onemolten metal grain transfer range nP1D and the one pulse to a pluralityof molten metal grains Δ1PnD which are positioned outside of the onepulse to one molten metal grain transfer range 1P1D. As a result, thepulse current value and the pulse duration can be extended to a enlargedrange. This makes it possible to enlarge the variation value of the arclength Le to extend the application field in various uses.

Embodiment 11, Description of FIG. 29

FIG.29 is a graph showing a molten metal transfer in connection with thepulse duration TP ms (horizontal axis) and the pulse current value Ip A(vertical axis) when the pulse MIG arc welding method is carried out byusing a stainless steel. Reference characters STR, Δ1PnD, 1P1D, nP1D andDPR are expressed in a similar way to that of FIG. 28 and accordingly,their description will be omitted.

In a pulse MAG arc welding method carried out by energizing the pulsewelding current obtained by switching between the first pulse currentgroup and the second pulse current group, a first welding method managesthe wire to be fed at constant feed rate determined in advance and thepulse current value, the pulse period, the pulse duration (pulseenergizing time) of each pulse of the first current group and a basecurrent value to be set to a value by which the molten metal transferfrom the consumable electrode to the welding material synchronizes withone of a plurality of pulse currents to form the plurality of pulses toone molten metal transfer mode. The pulse current value, the pulseduration and the pulse frequency of the second pulse group and the basecurrent are energized by a pulse welding current set to a valuedifferent from that of the first current group within a range to formthe one pulse to one molten metal transfer model. Then, the wireextension length between the terminal of the electric supplying tip andthe terminal of the wire is changed, while the arc length between theterminal of the wire and the surface of the welding material is switchedperiodically. When the arc length varies due to the unbalance betweenthe wire feed rate and the wire melting speed, the arc length isrecovered by changing the pulse period, the pulse duration, the basecurrent or the pulse current so that the pulse MAG arc welding iscarried out only by the spray transfer mode.

A second welding method is a method carried out by the one pulse toplurality of molten metal grains transfer mode in place of the one pulseto one molten metal grain transfer mode of the second pulse currentgroup described with the first welding method mentioned above.

A welding method is to carry out the welding within the range at whichthe slight short circuit generates as mentioned with FIGS. 24 and 25when the pulse current ratio of the first pulse current group isrelatively small or the arc length is short. The welding method mayadditionally carry out the welding within the one pulse to one moltenmetal grain transfer range excluding the range at which the slight shortcircuit generates.

Embodiment 12, Description of FIG. 31

FIG. 31 is a graph showing the molten metal transfer mode in connectionwith a pulse duration TP ms (horizontal axis) and the pulse currentvalue IP A (vertical axis) when the welding is carried out at thewelding current average value of Ia=100 A by switching periodicallybetween the first pulse current group and the second current group withan aluminum wire A5183 of 1.2 mm diameter. In FIG. 31, the relationshipamong the pulse current, the pulse duration and the molten metaltransfer mode is obtained by photographing the molten metal transferstate at a high speed and by waveform analysis. In FIG. 31, referencecharacters STR, Δ1PnD, 1P1D, nP1D and DRP denote the streaming transferrange, one pulse to plurality of molten metal grains transfer range, onepulse to one molten metal grain transfer range, a plurality of pulses toone molten metal grain transfer range and the short circuit transferrange in a similar way to those of FIG. 28.

The welding method is carried out by a setting condition of the firstpulse current group as shown in the following: The arc length is shortand in 2 mm. The pulse current value and the pulse duration at theplurality of pulse to one molten metal transfer range nP1D can beexpressed by points b, e, and f in FIG. 31, that is, 260 A-1.0 ms, 280A-0.8 ms, and 250 A-1.6 ms. Next, the second pulse current settingcondition is that the arc length is long and the pulse current value andthe pulse duration shown by a point a in the one pulse to one moltenmetal grain transfer range is 300 A-2.0 ms. The welding method iscarried out by switching between the first pulse current group and thesecond pulse current group. When the arc length Lt or Left and right MMis changed by changing the wire feed rate against the setting conditionof the first pulse current group, that is, points b, e, and f, thenumber of the short circuit Nst times/sec increases rapidly with adecrease in the arc length below 2 mm. Therefore, the arc length lowerthan 2 mm is not suitable for the application of the present invention.Accordingly, in the welding method according to the present invention,it is necessary to make the arc length longer than 2 mm at the firstpulse current group setting condition.

Embodiment 13, description of FIG. 32

FIG. 32 is a graph showing the molten metal transfer mode in connectionwith a pulse duration TP ms (horizontal axis) and the pulse currentvalue IP A (vertical axis) when the welding is carried out at thewelding current average value of Ia=120 A by switching periodicallybetween the first pulse current group and the second current group withan aluminum wire A5183 of 1.6 mm diameter. In FIG. 32, referencecharacters STR, Δ1PnD, 1P1D, nP1D and DRP denote the streaming transferrange, one pulse to plurality of molten metal grains transfer range, onepulse to one molten metal grain transfer range, a plurality of pulses toone molten metal grain transfer range and the short circuit transferrange in a similar way to those of FIG. 28.

The welding method is carried out by a setting condition of the firstpulse current group as shown in the following: The arc length is shortand in 3 mm. The pulse current value and the pulse duration at theplurality of pulse to one molten metal transfer range nP1D can beexpressed by a point d in FIG. 32, that is, 330 A-1.2 ms. Next, thesecond pulse current setting condition is that the arc length is longand the pulse current value and the pulse duration shown by c point inthe one pulse to one molten metal grain transfer range 1P1D are 370 Aand 2.0 ms, respectively. When the welding method is carried out byswitching the first pulse current group and the second pulse current, itis necessary to make the arc length longer than 2 mm at the first pulsecurrent group setting condition in a similar way to that of FIG. 31.

Embodiment 14, Description of FIG. 33

FIG. 33 is a graph showing the molten metal grain transfer mode in thesame way as that of FIG. 31. In the welding method the first pulsecurrent group setting condition is that the arc length is short and 2 mmand the pulse current value and the pulse duration in the plurality ofpulses to one molten metal grain transfer range can be expressed by apoint m in FIG. 33, that is, 260 A-1.0 ms. Next, the second pulsecurrent group setting condition is that the arc length is long, and thepulse current value and the pulse duration can be expressed by a point nin the one pulse to plurality of molten metal grains transfer range1PnD, that is, 350 A-1.8 ms. When the arc length is lower than 2 mmespecially 1.5 mm, the number of the short circuit rapidly increases. Asa result, the range of the arc length lower than 2 mm is not suitablefor the welding method according to the present invention. It isnecessary to make the arc length longer than 2 mm at the first pulsecurrent group setting condition in a similar way to that of FIG. 31.

Embodiment 15, Description of FIG. 34

FIG. 34 is a graph showing the molten metal grain transfer mode in thesame way as that of FIG. 32. In the welding method the first pulsecurrent group setting condition is that the arc length is short and 3mm, and the pulse current value and the pulse duration in the pluralityof pulses to one molten metal grain transfer range nP1D can be expressedby a point p in FIG. 34, that is, 360 A-1.0 ms. Next, the second pulsecurrent group setting condition is that the arc length is long, and thepulse current value and the pulse duration can be expressed by a point qin the one pulse to plurality of molten metal grains transfer range1PnD, that is, 400 A-2.0 ms. When the welding method is carried out byswitching the first current group and the second current group, it isnecessary to make the arc length longer than 2 mm at the first pulsecurrent group setting condition in a similar way to that of FIG. 33.

Description of FIG. 35

FIG. 35 is a graph showing the relationship between the average value ofthe arc welding current Ia A (horizontal axis) and the maximum value ofthe variation value of the arc length Le mm, in connection with awelding method within a switching range (referred to a project range)between a plurality of pulse to one molten metal grain transfer rangenP1D shown by a solid line C and a one pulse to one molten metal graintransfer range 1P1D and a welding method in a one pulse to one moltenmetal grain transfer range (1P1D) shown by a dotted line Z in a casewhen an aluminum wire A5183 of a diameter 1.2 mm is used. With referenceto FIG. 35, at the average value of the welding current Ia=60 A, thewelding method 1P1D shown by a dotted line has the maximum value of thearc length variation value Le Feibush mm whereas the welding methodwithin a project range has the maximum value of the arc length variationvalue Le=4 mm. Further, at the average value of the pulse current Ia=200A, the maximum value of the arc length according to the welding methodof 1P1D is Le=6 mm whereas the maximum value of arc length according tothe project range is Le=8 mm which is two times larger than that of thewelding method at 1P1D range. As a result, the welding method within theproject range can expand the application field to be carried out by thewelding method 1P1D in connection with the welding for the thin plateexecuted by a low current.

Description of FIG. 36

FIG. 36 is a graph showing the relationship between the average value ofthe arc welding current Ia A (horizontal axis) and the maximum value ofthe variation value of the arc length Le mm, in connection with awelding method within a project range shown by a solid line D and awelding method of 1P1D range shown by a dotted line in a case when astainless steel wire SUS308 of a diameter 1.2 mm is used. With referenceto FIG. 35, at the average value of the welding current Ia=60 A, thewelding method 1P1D has maximum value of the arc length variation valueLe=1.0 mm whereas the welding method within a project range has themaximum value of the arc length variation value Le Feibush mm. Further,at the average value of the pulse current Ia=200 A, the maximum value ofthe arc length according to the welding method of 1P1D is Le=4 mmwhereas the maximum value of arc length according to the project rangeis Le=8 mm which is two times larger than that of the welding method at1P1D range. As a result, the welding method within the project range canexpand the application field to be carried out by the welding method1P1D in connection with the welding for the thin plate executed by a lowcurrent.

In a pulse MAG arc welding method carried out by energizing the pulsewelding current obtained by switching between the first pulse currentgroup and the second pulse current group, a first welding method managesthe wire to be fed at constant feed rate determined in advance, and thepulse current value, the pulse period, the pulse duration (pulseenergizing time) of each pulse of the first current group and a basecurrent value to be set to a value by which the molten metal transferfrom the consumable electrode to the welding material synchronizes withone of a plurality of pulse currents to form the plurality of pulses toone molten metal transfer mode. The pulse current value, the pulseduration and the pulse frequency of the second pulse current group andthe base current are energized by a pulse welding current set to a valuedifferent from that of the first current group within a range to formthe one pulse to one molten metal transfer model. Then, the wireextension length between the terminal of the electric supplying tip andthe terminal of the wire is changed, while the arc length between theterminal of the wire and the surface of the welding material is switchedperiodically. When the arc length varies due to the unbalance betweenthe wire feed rate and the wire melting speed, the arc length isrecovered by changing the pulse period, the pulse duration, the basecurrent or the pulse current so that the pulse MAG arc welding iscarried out only by the spray transfer mode.

A second welding method is a method carried out by the one pulse toplurality of molten metal grains transfer mode in place of the one pulseto one molten metal grain transfer mode of the second pulse currentgroup described with the first welding method mentioned above.

A welding method is to carry out the welding within the range at whichthe slight short circuit generates as mentioned with FIGS. 24 and 25when the pulse current value of the first pulse current group isrelatively small or the arc length is short. A welding method is tocarry out the welding within the one pulse to one molten metal graintransfer range excluding the range shown in FIGS. 24 and 25 at which theslight short circuit generates.

Embodiment 16, Description of FIGS. 37 and 39

FIG. 37 is a graph showing the molten metal grain transfer mode in thesame way as that of FIG. 31. In welding method the first pulse currentgroup setting condition is that the arc length is short and 3 mm, andthe pulse current value and the pulse duration in the one pulse to onemolten metal grain transfer range 1P1D can be expressed by a point g inFIG. 37, that is, 280 A-1.2 ms. Next, the second pulse current groupsetting condition is that the arc length is long, and the pulse currentvalue and the pulse duration can be expressed by a point h in the onepulse to plurality of molten metal grains transfer range 1PnD, that is,350 A-1.8 ms.

When the welding method is carried out by switching between the firstcurrent group and the second current group, the first and second pulsecurrent groups are changed in the setting condition into points g and h,respectively so as to change the arc length to Lt and Left and rightwith the constant wire feed rate WF=500 cm/min. A graph shown in FIG. 39indicates the relationship between the average values of weldingcurrents during the first and the second pulses energizing times M1 andM2 A (horizontal axis) and the arc voltages Va1 and Va2 V (verticalaxis) corresponding to the average values of welding currents,respectively.

With reference to FIG. 39, at an operation point g of the first pulsecurrent IP1=280 A and the first pulse duration TP1=1.2 ms, the followingconditions are held; the arc length Lt Feibush mm, the first arc voltagevalue Val=18.5 V, and the average value of the welding current duringthe first pulse energizing time M1=97.5 A. At the operation point h ofthe second pulse current value IP2=350 A and the second pulse durationTP2=1.8 ms, the following conditions are held; the arc length Left andright=9 mm, the second arc voltage value Va2=20.0 V and the averagevalue of the welding current during the second pulse energizing timeM2=101.5 A.

When the first arc voltage setting circuit VS1 of the welding apparatusmanages the first arc voltage setting value Vs1 to cause the arc lengthof 9 mm, the pulse frequency or the base current value increases andmoves to an operation point g1 on the curve ga. At this point, the arcvoltage value is Va3=21.5 V, and the welding current value is 98.5 A. Itis interesting to compare the point g1 with a point h against the pointg. Without changing the pulse current and pulse duration, but withchanging the pulse frequency or the base current value, a variation fromthe point g to a point g1 requires the variation value 3 V in the arcvoltage. On the other hand, a variation from the point g to the point hwith changing the pulse current value and the pulse duration requiresthe variation rate in the welding current average value(101.5-97.5)/97.5×100=4.1% whereas the variation in the arc voltagevalue is only Va2-Va1=1.5 V. That is, when the arc length is changedfrom 3 mm to 9 mm, a variation from the point g to the point g1 requiresthe variation of 3 V in the arc voltage. However, a variation from thepoint g to the point h requires a slight increase (4%) in the weldingcurrent average value but a variation in the arc voltage of 1.5 V whichis half of the voltage required for the former case. This means that thevariation in the arc length from the point g to the point h results notonly in the variation in the arc voltage but also in the increase in thewire melting speed. Accordingly, at the point g, the increase in thewire melting speed permits the plurality of pulse to one molten metalgrain mode to be completed and hence, it is possible to hold the stablearc free from the short circuit. In FIG. 39, the straight lines Vg, Vhand Vi indicates the arc voltage obtained with the variation in thepulse frequency of the welding electric source or the variation in thebase current under keeping the pulse current value and pulse durationthe same as those of the operation points g, h and gl. Numerals 1, 5, 3,6, 9 and 12 on the curves and the lines of FIG. 39 how the arc lengthsmm at the operation points of output current values and the arc voltagevalues.

Embodiment 17, description of FIG. 38

FIG. 38 is a graph showing the molten metal grain transfer mode in asimilar way to FIG. 32. The welding method is carried out by a settingcondition of the first pulse current group as shown in the following:The arc length is short and in 3 mm. The pulse current value and thepulse duration at the plurality of pulse to one molten metal transferrange nP1D can be expressed by a point j in FIG. 38, that is, 330 A-1.2ms with the pulse current value-the pulse duration. Next, the secondpulse current setting condition is that the arc length is long and thepulse current value and the pulse duration shown by a point k in the onepulse to a plurality of molten metal grains transfer range 1PnD is 400A-2.0 ms. The welding method is carried out by switching between thefirst pulse current group and the second pulse current group.

Description of FIG. 40

FIG. 40 is a graph showing the relationship between the average value ofthe arc welding current Ia A (horizontal axis) and the maximum value ofthe variation value of the arc length Le mm, in connection with awelding method within a switching range (referred to a nP1D-1P1D range)between a plurality of pulse to one molten metal grain transfer rangenP1D shown by a solid line C and a one pulse to one molten metal graintransfer range 1P1D and a welding method in a one pulse to one moltenmetal grain transfer range (1P1D) shown by a dotted line Z in a casewhen an aluminum wire A5183 of a diameter 1.2 mm is used. With referenceto FIG. 35, at the average value of the welding current Ia=200 A, thewelding method 1P1D shown by a dotted line has the maximum value of thearc length variation value Le=6 mm whereas the welding method within aproject range has the maximum value of the arc length variation valueLe=8 mm. As a result, the welding method within the nP1D-1P1D range canexpand the application field to be carried out by the welding method1P1D.

A welding method is to change the first arc length Lt and the second arclength Left and right by switching the welding current valueperiodically.

The average value Ia of welding current in the pulse current can beexpressed by the following equation with reference to FIG. 11:

    Ia= IP×TP+IB(D-TP)!/D

where IP=pulse current, TP=pulse duration, IB=base current and D=pulseperiod (D=1/f; f is a pulse frequency).

Therefore, the average value Ia of welding current can be switched byswitching one of the IP, TP, IB and f with the switching frequency F.

Against the external disturbance due to the variation in the wire feedrate and the variation in the distance between the surface of thewelding material and the electric supplying tip, it is necessary to keepthe first arc length Lt and the second arc length Left and right at avalue within the range predetermined and to prevent the short circuit ortoo much enlargement of the arc length. In order to satisfy thisrequirement, it is necessary to change the average value of the weldingcurrent with the arc voltage control signal Cm2 obtained from thedifference between the arc voltage setting signal Vs1 and the arcvoltage detection signal Vd.

The average value of welding current Ia can be controlled by the abovef, TP, IB or IP. The change in the pulse frequency f3, pulse durationTP3, base current IB or pulse current IP3 can control the wire meltingspeed to maintain the first and second arc lengths.

The welding method can be carried out by the following four kinds ofmethods.

1. A case when the pulse frequency f3 is controlled with the arc voltagecontrol signal Cm3.

The first welding current I1 and the second welding current I2 areswitched by one, two or three combination of pulse current IP, pulseduration Tp and base current IB.

2. A case when the pulse duration TP3 is controlled by the arc voltagecontrol signal Cm2.

The first welding current I1 and the second welding current I2 areswitched by one, two or three combination of pulse current IP, pulsefrequency f and base current IB.

3. A case when the base current value IB3 is controlled by the arcvoltage control signal Cm2.

The first welding current I1 and the second welding current I2 areswitched by one, two or three combination of pulse current IP, pulseduration TP and pulse frequency f.

4. A case when the pulse current value IP3 is controlled by the arcvoltage control signal Cm2.

The first welding current I1 and the second welding current I2 areswitched by one, two or three combination of pulse duration TP, pulsefrequency f and base current value IB.

A difference between a second welding method described hereinbelow andthe welding method described immediately above is as follows: In thewelding method described immediately above, the arc voltage settingsignal Vs1 is used in common to the first arc length and the second arclength. On the other hand, in the second welding method, the first arclength Lt is set by the first arc voltage setting signal Vs1 and thesecond arc length Left and right is set by the second arc voltagesetting signal Vs2.

In the welding method described immediately above, in order to switchingbetween the first arc length Lt and the second arc length Left andright, it is necessary to switch at least one setting value selectedfrom the group of pulse frequency f, pulse duration TP, base currentvalue and pulse current value IP. On the other hand, in the secondwelding method, the first arc voltage setting signal Vs1 and the secondarc voltage setting signal Va2 are switched to each other. Hence, thefirst welding current value is controlled by the first arc voltagecontrol signal Cm2 obtained with the difference between the first arcvoltage setting signal Vs1 and the arc voltage detection signal Vd,whereas the second welding current value I2 is controlled by the secondarc voltage control signal Cm2 obtained with the difference between thesecond arc voltage setting signal Vs2 and the arc voltage detectionsignal Vd.

As a result, the first arc voltage control signal Cm2 controls the pulsefrequency f31, pulse duration TP31, base current IB31 or pulse currentvalue IP31, while the second arc voltage control signal Cm2 controls thepulse frequency f32, pulse duration TP32, base current IB32 or pulsecurrent value IP32.

Accordingly, in the second welding method it is necessary to switchbetween the first arc voltage setting signal Vs1 and the second arcvoltage setting signal Vs2. However, with the welding method describedimmediately above, it is not always necessary to switch the settingsignal for the pulse current value IP, pulse duration TP, pulsefrequency f or base current value IB.

For the purpose of expanding the application field of the second weldingmethod the switching method similar to that of the method describedimmediately above can be used for switching one, two or three settingsignals for the pulse current value IP, pulse duration TP, pulsefrequency f and base current value IB.

In another welding method, the first arc voltage value Va1 and thesecond arc voltage value Va2 are 0.3 or 4 V and are narrow in theadjustment range. The variation value of the arc length Le is largelyaffected by the variation value of the arc voltage ΔVa. Accordingly, thefirst arc voltage setting value Vs1 and the second arc voltage settingvalue Vs2 must be monotonously adjusted.

The welding method thus described is to memorize the second arc voltagesetting value Vs2 corresponding to the first voltage setting Vs1 andthen to read out the second arc voltage setting value Vs2 correspondingto the first arc voltage setting Vs1 determined in advance in order toenergize the first pulse current group and second pulse current group.

In another welding method, the suitable setting values of the first arcvoltage value Va1 and the second arc voltage value Va2 are determined inconnection with the wire feed rate.

The welding method thus described is to memorize in advance the firstarc voltage setting value Vs1 corresponding to the wire feed rate Wf andto memorize the second arc voltage setting value Vs2 corresponding tothe first arc voltage setting value Vs1. Then, the welding method is toread out the first arc voltage setting value Vs1 corresponding to thepredetermined wire feed rate setting value Wf and the second arc voltageVs2 corresponding to the first arc voltage setting value Vs1 and then toenergize the first and the second pulse current groups.

Description of FIGS. 41 and 42

FIG. 41 is a graph showing the relationship between the welding currentvalue I A (horizontal axis) and the arc voltage V (vertical axis) whenthe pulse MAG arc welding method is carried out with an aluminum alloy5052 plate of 5 mm thickness at a wire feed rate WF5=500 cm/min andWF7=700 cm/min by using an aluminum alloy 5183 of 1.2 mm diameter.

FIG. 42 is a data table in which the first arc voltage setting valuesUn=U1, U2 . . . are predetermined in connection with the wire feed ratesWn=W1, W2 . . . when the wires are fed at predetermined wire feed ratesand another data table in which the second arc voltage setting valuesVn=V1, V2 . . . are predetermined in connection with the first arcvoltage setting values Un=U1, U2 . . .

First, with reference to FIGS. 41 and 42, the standard data formationwill be described with the curve WF5=500 which is directed to a wirefeed rate of 500 cm/min in connection with the formation of the table ofdata to be memorized among the data included. In order to determine theoperation point on this curve, it is necessary to determine the arclength corresponding to the arc voltage. When it is determined that thefirst arc voltage value is Val=17 V, the operation point is a point Q11.The program determines the arc voltage setting value Un=U1, U2 . . . Unfor obtaining the first arc voltage value Va1 corresponding to the wirefeed rate in respect to the wire feed rates Wn=W1, W2 . . . Wn as shownin the upper table of FIG. 42 and memorizes these data. Next, when it isdetermined that the variation value ΔVa of the arc voltage is, forexample, 2.5 V, the second arc voltage value is determined as follows;

    Va2=Va1+ΔVa=17+2.5=19.5V

and then the operation point is Q12. The program further determinessecond arc voltage setting values Vn=V1, V2 . . . Vn for obtaining thesecond arc voltage Va2=V1 in response to the first arc voltage settingvalues Un=U1, U2 . . . Un memorized in advance as shown in the lowertable in FIG. 42 and memorizes these data. The relationship among thesetting values of Wn, Un, and Vn are predetermined in the following way;for example, W5 is a wire feed rate of 500 cm/min; U5 is an arc voltageof 17 V (operation point Q11); V5 is an arc voltage of 19.5 V (operationpoint Q12). In a similar way to the above, the following arepredetermined; W7 is a wire feed rate of 700 cm/min; U7 is an arcvoltage of 19.3 V (operation point Q21); V7 is an arc voltage of19.3+2.5=21.8 V (operation point Q22).

The following description will be directed to a method that the programreads out the memorized data as shown in FIG. 42 and controls the firstand the second voltages Va1 and Va2. When Wn=W5 is selected from thewire feed rates Wn=W1, W2 . . . Wn in FIG. 42, the wire feed rate is 500cm/min. The program reads out the first arc voltage setting value U5from the first arc voltage setting values Un=U1, U2, . . . Un in acorresponding way to the setting value W5 and controls the first arcvoltage shown by an operation point Q11 to be 17 V. Further, the programreads out the second arc voltage setting value V5 corresponding to thesetting value U5 and controls the second arc voltage shown by anoperation point Q12 to be 19.5 V. When Wn=W7 is selected, the wire feedrate is 700 cm/min. The program reads out the first arc voltage settingvalue U7 in a corresponding way to the setting value W7 and controls thefirst arc voltage shown by an operation point Q21 to be 19.3 V. Further,the program reads out the second arc voltage setting value V7corresponding to the setting value U7 and controls the second arcvoltage shown by an operation point Q22 to be 21.8 V.

The basic welding method according to the present invention is to switchthe welding electric source between the first welding current value andthe second welding current value with the wire feed rate at a constantvalue as described above and to change the welding current ratio betweenI2 and I1 within the narrow range of 1.03 to 1.10.

The additional welding method according to the present invention is toincrease the wire melting amount to improve the reinforcement inaddition to the basic welding method according to the present invention.Accordingly, the additional welding method is to switch the wire feedrate between the first wire fed rate and the second wire feed rate atthe switching frequency F=0.5 to 5 Hz and to change the ratio of thesecond welding current value I2 to the first current value I1 within thenarrow range of 1.05 to 1.20.

The switching of the wire feed rate according to the prior art has beenpractically carried out at only 3 Hz due to the mechanical inertiabecause the variation value in the wire feed rate has been large. Theadditional welding method according to the present invention can bepractically carried out at the switching frequency of 5 Hz because thevariation in the wire feed rate is low. It is noted that when the ratioof the second current value I2 to the first current value I1 is high,the effect according to the basic welding method of the presentinvention is decreased. Therefore, it is necessary to hold the ratio ina range between 1.05 and 1.20.

A welding method of another embodiment is to switch between the firstwire feed rate setting signal Im1 and the second wire feed rate settingsignal Im2 and between the first arc voltage setting signal Vs1 and thesecond arc voltage setting signal Vs2 at the switching frequency F.Then, the first pulse current group is energized by controlling thepulse frequency f31, pulse duration TP 31, base current value IB31 orpulse current value IP31 with the arc control signal Cm2 obtained withthe difference between the first arc voltage setting signal Vs1 and thearc voltage detection signal Vd. Further, the second pulse current groupis energized by controlling the pulse frequency f32, pulse duration TP32, base current value IB321 or pulse current value IP32 with the arccontrol signal Cm2 obtained with the difference between the second arcvoltage setting signal Vs2 and the arc voltage detection signal Vd.

The welding method of another embodiment is a method which memorizes thesecond arc voltage setting values Vs2 corresponding to the first arcvoltage setting values Vs1 at the wire feed rates Im2 and energizes thefirst pulse current group and the second current group by reading outthe second arc voltage setting values Vs2 corresponding to the first arcvoltage setting values Vs1 determined in advance.

The welding method of another embodiment is a method which memorizes thefirst arc voltage setting values Vs1 corresponding to the first wirefeed rate setting values Im1, memorizes the second arc voltage settingvalues Vs1 corresponding to the first arc voltage setting values Va1 atthe second wire feed rates Im2 and energizes the first pulse currentgroup and the second current group by reading out the first arc voltagesetting values Vs1 corresponding to the first wire feed rates Im1determined in advance, and the second arc voltage setting values Vs2corresponding to the second wire feed rates Im2 determined in advance.

Description of FIG. 43

FIG. 43 is a data table in which the first arc voltage setting valuesUn=U1, U2 . . . Un are predetermined in connection with the wire feedrates Wn=W1, W2 . . . Wn when the MAG arc welding method is carried outby feeding wires at a rate obtained by switching periodically betweenthe first and the second wire feed rates determined in advance andanother data table in which the second arc voltage setting values Vn=V1,V2 . . . are predetermined in connection with the first arc voltagesetting values Un at the second wire feed rates Xn=X1, X2 . . . Xn.

First, with reference to FIGS. 41 and 43, the standard data formationwill be described with the curve WF5=500 which is directed to a wirefeed rate of 500 cm/min in connection with the formation of the table ofdata to be memorized. In order to determine the operation point on thiscurve, it is necessary to determine the arc length corresponding to thearc voltage. When it is determined that the first arc voltage value isVal=17 V, the operation point is a point Q11. The program determines thearc voltage setting value Un=U1, U2 . . . Un for obtaining the first arcvoltage value Va1 corresponding to the wire feed rate in respect to thewire feed rates Wn=W1, W2 . . . Wn as shown in the upper table of FIG.42 and memorizes these data. Next, when it is determined that thevariation value ΔVa of the arc voltage is, for example, 2.5 V, thesecond arc voltage value is determined as follows;

    Va2=Va1+ΔVa=17+2.5=19.5 V

The second arc voltage value Va2 is corresponding to the operation pointQ12 on the curve WF5=500 having the operation point Q12 of the first arcvoltage value Va1, and is a different value when switched to the secondwire feed rate in a similar way to the welding method described above.For example, when the second wire feed rate is 700 cm/min and expressedby a curve WF7=700, the operation point Q12 on the curve WF5=500 becomesan operation point Q22 on the curve VF=700. Therefore, in order todetermine the operation point of the second arc voltage value at thesecond wire feed rate, it is necessary to obtain both of the first arcvoltage value and the second wire feed rate. That is, the second arcvoltage setting values Vn=V1, V2 . . . Vn must be determined from thefirst arc voltage setting values Un=U1, U2 . . . Un and the second wirefeed rates Xn=X1, X2 . . . Xn. The program determines the second voltagesetting values Vn=V1, V2 . . . Vn corresponding to the first arc voltagesetting values Un=U1, U2 . . . Un in a way as follows: The second arcvoltage setting values Vn=V11, V12 . . . V1n for the Xn=X1; Vn=V21, V22. . . Vn2 for the Xn=X2; VN=Vn1, Vn2 . . . Vnn for the Xn=Xn. These dataare memorized. The relationship among the setting values of Wn, Un, andXn are predetermined in the following way; for example, W5 is a wirefeed rate of 500 cm/min; U5 is an arc voltage of 17 V (operation pointQ11); W7 is a wire feed rate of 700 cm/min; U7 is an arc voltage of 21.8V (operation point Q22).

The following description will be directed to a method that the programreads out the memorized data as shown in FIG. 43 and controls the firstand the second voltages Va1 and Va2. When Wn=W5 is selected from thewire feed rates Wn=W1, W2 . . . Wn in FIG. 42, the wire feed rate is 500cm/min. The program reads out the first arc voltage setting value U5from the first arc voltage setting values Un=U1, U2, . . . Un in acorresponding way to the setting value W5 and controls the first arcvoltage shown by an operation point Q11 to be 17 V. Further, when theprogram reads out Xn31 X7 from the second wire feed rate setting valuesXn=X1, X2 . . . Xn, the second wire feed rate is 700 cm/min. The programreads out the second voltage setting value Vn=V75 from this settingvalue X7 and the setting value U5 read out previously and controls thesecond arc voltage shown by the operation point Q22 to be 21.8 V.

Description of FIG. 44

FIG. 44 is a graph showing the relationship between the variation valueLe in the arc length between the first arc length Lt and the second arclength Left and right (vertical axis) and the switching frequency F(horizontal axis) in a range between 0.5 to 25 Hz necessary forgenerating the vibration at the molten metal pool to obtain the effectof the present invention when the MIG welding method according to thepresent invention is carried out with an aluminum AL plate.

In FIG. 44, a solid line indicates the lower limit of the variationvalue Le in the arc length for generating the vibration at the moltenmetal pool in order to obtain the effect of the present invention.Positions of F=0.5 Hz, F=12 Hz and F=25 Hz require the variation valuesLe more than Le=2.5 mm, Le=1 mm and Le=0.5 mm, respectively. In thewelding for aluminum, the molten aluminum pool has a resonance frequencyFr of 20 to 25 Hz. Therefore, when the switching frequency F is morethan 15 Hz, the resonance vibration permits the molten aluminum pool tovibrate sufficiently with the variation value Le of the arc length in asmall value of 0.5 mm.

Embodiment 18

The embodiment 18 is an embodiment of pulse MIG arc welding method foran aluminum plate according to the present invention.

Description of FIG. 45

FIG. 45 is a graph having the average value of the welding current Ia A(referred to welding current I hereinafter) plotted at the horizontalaxis and the average value of the arc voltage Va V (referred to arcvoltage V hereinafter) plotted at the vertical axis and showing thesectional form of the welding beads and the arc length as a function ofIa and Va. In connection with FIG. 45, the welding condition is asfollows: An aluminum alloy A5052 plate in a thickness of 12 mm is weldedat a welding seed of 25 cm/min by using an aluminum alloy A5183 wire ina diameter of 1.2 mm as a consumable electrode.

With reference to FIG. 45, the welding condition is changed, forexample, from the first welding condition shown by a symbol A of weldingcurrent=100 A, arc voltage=19 V and arc length=3.5 mm to the secondwelding condition shown by a symbol B of welding current=150 A which islarger by 50% than the former and arc voltage=19.5 V. The apparent arclength at the second welding condition shows 3.5 mm which is the same asthat of the first welding condition. Further, there is no significantdifference in the sectional form of the welding bead between theposition of a symbol A and the position of symbol B. This means that itis not possible for this method to obtain the scale bead in regularripple pattern in a similar way to that of the TIG filler arc weldingmethod.

On the other hand, the welding condition is changed from the firstwelding condition shown by a symbol A to the second welding conditionshown by a symbol C at which the welding current is 100 A the same asthat of the first welding condition and the arc voltage is increased to20 V by adding 1 V. The arc length at the symbol C is increased to 6 mmwith an increment of 2.5 mm. There is a significant difference in thesectional form of the welding bead between the position of the symbol Aand the position of the symbol C. This means that it is possible forthis welding method to obtain the scale bead in regular ripple patternin a similar way to the TIG filler arc welding method. In such a way, itis possible to obtain the scale bead in regular ripple pattern byincreasing the apparent arc length by a size more than 2.5 mm betweenthe first welding condition and the second welding condition.

Description of FIG. 46

FIG. 46 is a graph showing whether the scale bead in regular ripplepattern is formed or not as a function of the relationship between thewelding current I A (horizontal axis) and the arc length variation valueLe mm (vertical axis). With reference to FIG. 46, a symbol×indicates arange at which the scale bead is not formed and the arc length variationvalue is 1 to 2 mm, a symbol Δ indicates a range at which the scale beadis not in regular ripple pattern and the arc length variation value is 2mm and a symbol≠ indicates a range at which the scale bead in regularripple pattern is obtained in a similar way to the TIG filler arcwelding method and the arc length variation value is more than 2.5 mm.

When an aluminum plate is welded with the pulse MIG arc welding methodto change the arc length according to the present claim, it is possibleto obtain the scale bead shown in FIG. 47. The welding condition at thistime is as follows: The welding material is an aluminum alloy A5052plate in a thickness of 12 mm. A consumable electrode is an aluminumalloy A5183 wire in a diameter of 1.2 mm. The welding is carried out byswitching between the first welding condition of welding current 140 Aand the arc voltage 20.0 V and the second welding condition of weldingcurrent 170 A and arc voltage 23.0 V with a switching frequency 2 Hz ata welding speed 40 cm/min. Since the MIG arc welding method executed onan aluminum material with an aluminum consumable electrode of 1.2 mmdiameter has a critical current of 150 A, the pulse MIG arc weldingmethod is adapted for the purpose of using only the spray transfer modewithout the short circuit transfer mode.

According to the above description, since the welding current value ofthe one or both welding conditions is lower than the critical currentcorresponding to the diameter of the wire, the welding is carried out bythe pulse MIG arc welding method for obtaining the spray transfer mode.When the both of the welding conditions have the welding current higherthan the critical current, it is possible for the flat dc current toobtain the scale bead in regular ripple pattern in a similar way to theTIG filler arc welding method. The embodiment for this case is shown asfollows: The welding material is an aluminum alloy A5052 plate in athickness of 12 mm. A consumable electrode is an aluminum alloy A5183wire in a diameter of 1.2 mm. The welding is carried out by keeping thewelding current at a constant value of 180 A higher than the criticalcurrent value and switching between the arc voltages of 22 V and 24 Vwith a switching frequency 2 Hz at a welding speed 40 cm/min. As aresult, the arc length variation value is 4 mm. It is possible to obtainthe scale bead in regular ripple pattern.

Embodiment 19

The embodiment 19 is aimed at the pulse MIG arc welding method forcopper. In the MIG arc welding for copper, copper has a melting point of1085° C. which is higher than that of aluminum. In addition, copper hasa thermal conductivity of 0.95 cal/cm.sec.° C. which is larger than 0.53cal/cm.sec.° C. of aluminum and has a high thermal diffusion coefficientto permit the molten copper to solidify rapidly. Accordingly, the moltencopper pool enlarged with the variation in the arc length solidifies asit is and forms the scale bead after movement of the arc. A pure copperplate in a thickness of 6 mm is preheated at 400° C. and is subjected tothe MIG arc welding method with the pure copper consumable electrode of1.2 mm diameter by switching periodically between the arc voltages 22 Vand 25 V with a switching frequency 2 Hz at a welding current of 200 Aand a welding speed of 35 cm/min. It is possible to obtain the scalebead the same as that shown in FIG. 47.

Description of FIG. 48

FIG. 48 is a graph having the average value of the welding current Ia Aplotted at the horizontal axis and the average value of the arc voltageVa V plotted at the vertical axis and showing the sectional form of thewelding beads and the arc length obtained with the MIG arc weldingmethod. In connection with FIG. 48, the welding condition is as follows:A copper plate in a thickness of 10 mm is preheated at a temperature of400° C. and is welded at a welding seed of 25 cm/min by using a copperconsumable electrode in a diameter of 1.2

With reference to FIG. 48, the welding condition is changed, forexample, from the first welding condition shown by a symbol A of weldingcurrent=200 A, arc voltage=22 V and arc length=3 mm to the secondwelding condition shown by a symbol B of welding current=300 A which islarger by 50% than the former and arc voltage=23 V. When the apparentarc length at the second welding condition shows 3 mm which is the sameas that of the first welding condition, there is no significantdifference in the sectional form of the welding bead between theposition of a symbol A and the position of symbol B. This means that itis not possible for this method to obtain the scale bead in regularripple pattern in a similar way to that of the TIG filler arc weldingmethod. On the other hand, the welding condition is changed from thefirst welding condition shown by a symbol A to the second weldingcondition shown by a symbol C at which the welding current is 200 A thesame as that of the first welding condition and the arc voltage isincreased to 23.5 V by adding 1.5 V. The arc length at the symbol C isincreased to 6 mm with an increment of 3 mm. There is a significantdifference in the sectional form of the welding bead between theposition of the symbol A and the position of the symbol C. This meansthat it is possible for this welding method to obtain the scale bead inregular ripple pattern in a similar way to the TIG filler arc weldingmethod. In such a way, it is possible to control the penetration shapeby changing alternatively the sectional form of the bead by increasingthe apparent arc length by a size more than 3 mm between the firstwelding condition and the second welding condition.

The appearance of the bead is determined by the relationship between thewelding speed WS cm/min and the switching frequency F Hz shown inTable 1. In general, the pitch Pt mm of the scale bead shown in FIG. 47is governed by the following equation;

    Pt=WS/60F

The conventional TIG filler arc welding method generates the scale beadin regular ripple pattern having a pitch Pt 1 to 5 mm . As a result, inview of the relationship between the above equation and the Table 1, itis possible for the MAG welding method according to the present claim toobtain the scale bead in regular ripple pattern in a similar way to thatof the TIG filler arc welding method even with the welding speed higherthan that of the TIG filler arc welding method. For example, in a casewhen the welding speed WS=180 cm/min and the switching frequency F=15 Hz, the pitch Pt is 2 mm . In a case when WS=300 cm/min, and the switchingfrequency f=15 Hz , the pitch Pt is 3.3 mm.

Embodiment 20 . . . Description of FIG. 49

The embodiment is aimed at the pulse MIG arc welding method with astainless steel. FIG. 49 is a graph having the average value of thewelding current Ia A plotted at the horizontal axis and the averagevalue of the arc voltage Va V plotted at the vertical axis and showingthe sectional form of the welding beads and the arc length obtained withthe MIG arc welding method. In connection with FIG. 49, the weldingcondition is as follows: A stainless steel SUS304L plate in a thicknessof 8 mm is welded at a welding speed of 25 cm/min by using a stainlesssteel SUS308 in a diameter of 1.2 mm.

With reference to FIG. 49, the welding condition is changed, forexample, from the first welding condition shown by a symbol A of weldingcurrent=100 A, arc voltage=18 V and arc length=3 mm to the secondwelding condition shown by a symbol B of welding current=170 A which islarger by 70% than the former and arc voltage=18.3 V. When the apparentarc length at the second welding condition shows 3 mm which is the sameas that of the first welding condition, there is no significantdifference in the sectional form of the welding bead between theposition of a symbol A and the position of symbol B. On the other hand,the welding condition is changed from the first welding condition shownby a symbol A to the second welding condition shown by a symbol C atwhich the welding current is 100 A the same as that of the first weldingcondition and the arc voltage is increased to 19.5 V by adding 1.5 V.The arc length at the symbol C is increased to 6 mm with an increment of3 mm . There is a significant difference in the sectional form of thewelding bead between the position of the symbol A and the position ofthe symbol C. In such a way, it is possible to control the penetrationshape by changing alternatively the sectional form of the bead byincreasing the apparent arc length by a size more than 3 mm between thefirst welding condition and the second welding condition.

A steel such as stainless or alloy steel has a thermal conductivity in alow size, for example, iron has a thermal conductivity of 0.14cal/cm.sec.° C. which is greatly lower than those of aluminum andcopper. Therefor, it is difficult for the steel to obtain the scale beadin a similar way to that of aluminum or copper. However, the steelmaterial has the oxide film adhered thereto more weakly than aluminumand does not cause the arc to fly far away to the oxide film. The actualarc length is nearly equal to the theoretical arc length. Accordingly,with the steel material, it is possible to control the apparent arclength by adjusting the arc voltage. Hence, the periodic change in thearc voltage makes it possible to obtain the penetration shape differedfrom the conventional single form by melting together a plurality ofbead sectional form and the reinforcement.

A welding method of another embodiment is to carry out a butt weldingwith the maximum gap value 3.0 mm at the welding speed of 30 cm/min andthe maximum gap value of 1.5 mm at the welding speed of 100 cm/min withthe switching frequency of 0.5 to 15 Hz and the variation value Le ofarc length more than 3 mm.

Embodiment 21 . . . Description of FIGS. 50 and

FIG. 50 is a graph having the gap G mm of the butt at the welding lineplotted at a vertical axis and the welding speed WS cm/min plotted at ahorizontal axis and showing a range (shown by a oblique line) at whichthere is no melt down and a capability of welding when the welding speedis changed between 30 and 100 cm/min and the gap is also changed from0.5 to 3 mm in connection with a butt welding for an aluminum alloyA5052 plate of 1.5 mm thickness. In FIG. 50, a symbol x and a one pointchain line show the upper limit of the gap capable of being welded whenthe welding is carried out with the variation in the welding speed atthe pulse current value of 280 A and the pulse duration 1.2 ms under theconventional unit pulse mode (one pulse to one molten metal graintransfer mode) by taking the average value of welding current 60 to 100A. At the welding speed in a low speed of 30 cm/min, the gap of 2.0 mmis a upper limit for the welding. At the welding speed higher than 30cm/min, the upper limit is lowered. With the welding speed of 80 cm/minthe upper limit for the welding gap is decreased to 0.5 mm . After thefirst pulse current group is energized under lowering the arc voltage to16.5 to 18.5 V at the one pulse to one molten metal grain transfer modeby using the first pulse current comprising the pulse current value 280A and pulse duration 1.2 ms shown in FIG. 51 in a way shown by a symbolΔ and a dotted line, the pulse arc welding is carried out by increasingthe pulse current to 380 A and at the same time energizing the secondpulse current group controlled by a pulse period to maintain the onepulse to one molten metal grain transfer mode. Even with a gap of 3 mm ,it is possible to carry out the welding without the melt down at awelding speed of 30 cm/min. Even when the welding speed is 100 cm/min, agap of 1.5 mm can be welded. The reason for the high speed welding evenwith the gap can be explained by taking the following case that the highspeed welding is carried out by decreasing the arc length with the onepulse to one molten metal grain transfer mode. When the arc length isenlarged by increasing the pulse current value, pulse duration or theboth of them even with the gap of butt joint, the welding material atthe vicinity of the gap is melted by the expansion of the arc to an areawider than the gap. It is possible to prevent the melt down and toelevate the limit for the high speed welding by making the arc lengthshorter and building up the gap area.

A welding method of another embodiment is to carry out the lap weldingunder the following conditions: the switching frequency is 0.5 to 15 Hz;the arc length variation value is more than 3 mm ; the gap maximum valueis 3 mm at the welding speed 30 cm/min; the gap maximum value is 2 mm atthe welding speed 100 cm/min.

Embodiment 22 . . . Description of FIGS. 52 and

FIG. 52 is a graph having a gap G mm of lap joint at the welding lineplotted at a vertical axis and a welding speed WS cm/min plotted at ahorizontal axis and showing a range (shown by a oblique line) at whichthe welding can be carried out without melt down when the welding speedis changed from 30 to 90 cm/min and the gap is also changed from 1 to 3mm in connection with the lap welding for aluminum alloy A5052 plate ina thickness of 1.5 mm . In FIG. 52, a symbol x and a one point chainline show the upper limit of the gap capable of being welded when thewelding is carried out with the variation in the welding speed at thepulse current value of 280 A and the pulse duration 1.2 ms under theconventional unit pulse mode (one pulse to one molten metal graintransfer mode) without switching the pulse by taking the average valueof welding current 60 to 100 A. At the welding speed in a low speed of30 to 60 cm/min, the gap of 2.0 mm is a upper limit for the welding. Atthe welding speed higher than the above value, the upper limit islowered. With the welding speed of 90 cm/min, the upper limit for thewelding gap is decreased to 1 mm. After the first pulse current group isenergized under lowering the arc voltage to 16.5 to 18.5 V at the onepulse to one molten metal grain transfer mode by using the first pulsecurrent comprising the pulse current value 280 A and pulse duration 1.2ms shown in FIG. 51 in a way shown by a symbol Δ and a dotted line, thepulse arc welding is carried out by increasing the pulse current to 380A and at the same time energizing the second pulse current groupcontrolled by a pulse period to maintain the one pulse to one moltenmetal grain transfer mode. Even with a gap of 3 mm , it is possible tocarry out the welding without the one side melt down at the upper plateat a welding speed of 20 to 45 cm/min. Even when the welding speed is 60to 90 cm/min, a gap of 2 mm can be welded. The reason for the high speedwelding even with the gap can be explained by taking the following casethat the arc length at the second pulse duty period T2 is longer thanthat of the first pulse duty period. In addition, this pulse currentvariation value can maintain the one pulse to one molten metal graintransfer mode by changing slightly the pulse period and can prevent thearc length from being too much long. The second pulse current grouphaving the long arc length melts the upper and lower plates. The firstpulse current group having the short arc length causes the arc force tobe weak and builds up the gap with the molten metal. This prevents theone side melt down at the upper plate and increases the number of thegap which can be welded. Accordingly, it is possible to prevent the oneside melt down at the upper plate even when the upper plate is deformedinto a wave form with the thermal stress generated during the welding.

A welding method includes the step of switching the energizing ratiobetween the first welding current energizing time T1 and the secondwelding current energizing time T2; Ds=T1/(T1+T2)

A welding method includes the step of charging the energizing ratio Dsin accordance with the voltage detection value Vd.

The following description will be directed to the welding methodincluding the changing step which is applicable for the butt welding andthe lap welding.

The welding method manages the arc length to recover when the arc lengthvaries with the external disturbance as described above. The weldingmethod has been much improved in the tolerance of the gap size inconnection with a process to prevent the melt down due to the gap ofbutt joint or to prevent the melt down at the upper plate when there isa gap at the lap joint or a gap due to the thermal deformation.

In such a way, the variation in the gap causes the variation in the arclength. However, the welding method is not provided with a circuit forcorrecting the variation in the arc length resulted from the variationin the gap and therefore the rated phenomenon will be described in thefollowing.

Problem at the time of gap variation of butt welding . . . Descriptionof FIGS. 54 and 55

With reference to FIGS. 54 (A) to (E), the following description will bedirected to the phenomenon when the gap of butt joint becomes larger.

As shown by FIG. 54 (D), when the pulse current P1 is energized by aperiod determined by a frequency f1, it is assumed that a wire extensionlength between the terminal 4a of a electric supplying tip and theterminal of the wire 1a is denoted by La when there is the gap G1 ofbutt joint as shown in FIG. 54 (A). A reference character L0 denotes anactual arc length; a reference character W1, a molten metal pool width;and a reference character A1, an outside diameter of the arc.

Next, as shown by FIG. 54 (E), when the pulse current P1 of the firstpulse current group is energized by a period D1 determined by afrequency f1, the gap of the butt joint increases in the size. After theincrease in the gap, the wire extension length becomes La. The increasein the gap G2 results in the increase in molten metal pool width W2.Since the arc flies to the outside of the molten metal pool width W2,the outside diameter of the arc increases to a size A2. Accordingly, theactual arc length increases from L0 to L1 to increase the arc voltage.The arc voltage detection circuit VD detects the increase in the arcvoltage and causes the pulse frequency to decrease from f1 to f2. As aresult, the period of the pulse current P1 is increased as shown by acharacter D2 of FIG. 54 (E). Accordingly, the melting speed of the wirebecomes lower and the wire extension length becomes longer.

The wire extension length is increased to a length La+ΔL as shown inFIG. 54 (C) while the actual arc length decreases from L0 to L3 and thenthe arc voltage decreases. At the state shown in FIG. 54 (C), the wireterminal 1a is very close to the surface of the molten metal pool 2a,that is, the arc length is very short. When the state shown in FIG. 54(C)continues, the wire terminal puts into the molten metal pool togenerate the arc cutting. Further, there occurs the melt down caused bythe partial melting of one side of welding plates.

In FIG. 54 (B), the arc easily flies on the oxide film. It is noted thatan aluminum oxide is easily formed on aluminum metal. The arc flies onthe outside of molten metal pool having the oxide film rather than theinside of the molten metal pool having no oxide film. This causes theactual arc length to be longer than the theoretical arc length toincrease the arc voltage.

With reference to FIGS. 55 (A) to (D), the following description will bedirected to the phenomenon when the gap of butt joint is smaller.

As shown by FIG. 55(A), a wire extension length La is actually L0; themolten metal pool width, W1; and the outside diameter of the arc, A1.

Next, as shown in FIG. 55 (B), the gap of butt joint G3 decreases andthe wire extension length is La after the decrease in the gap. As shownin FIG. 55 (C), the decrease in the gap causes an increase in the moltenmetal pool width and the reinforcement. The increase in thereinforcement causes the arc to fly on the outside of the molten metalpool width W3. Thus, the actual arc length L5 is larger than L0 toincrease the arc voltage.

In FIG. 55 (B), the outside diameter A1 of the arc is larger than themolten metal pool width W1. In FIG. 55 (C), the outside diameter A3 islarger than the molten metal pool width W3. Further in view of FIGS. 55(B) and (C), W1<W3 and then finally A3≠A1. The actual arc length L5shown in FIG. 55 (C) is larger than the arc length L0 shown in FIG. 55(A) to increase the arc voltage.

When this state continues, the detection circuit controls the arc lengthto become shorter by detecting the increase in the arc voltage. Then,the wire extension length shown in FIG. 55 (A) is larger than La andbecomes to La+Δ L as shown in FIG. 55 (D). Finally, the wire terminal 1ais in contact with the surface 2a of the reinforcement to cause the arccutting or a number of the generation of spatter.

Problem at the time of gap variation of the lap welding . . .Description of FIGS. 56 and 57

FIGS. 56 (A) to (C) are structural model views illustrating thephenomenon when the gap of lap joint becomes larger. FIGS. 56 (D) and(E) are graphs showing the time passage of the period of pulse currentscorresponding to FIGS. 56 (A) and (B), respectively.

FIGS. 57 (A) to (D) are structural model views illustrating thephenomenon when the gap of lap joint becomes smaller.

The description with the phenomenon for the variation in the gap of lapjoint shown in FIGS. 56 (A) to (E) and FIGS. 57 (A) to (D) is the sameas that of the phenomenon for the variation in the gap of butt jointshown in FIGS. 54 (A) to (E) and FIGS. 55 (A) to (D) by exchanging theword `butt plane` to `lap plane` and should be omitted.

Correction method at the time of gap variation

A welding method described above is first to detect the change in thearc voltage when the variation in the arc length occurs with theunbalance between the wire feed rate and wire melting speed due to theexternal disturbance. Then, the wire melting speed is changed bychanging the pulse frequency with the circuit in a high response time.In addition to the effect to recover rapidly the arc length, the weldingmethod is to detect the variation in the arc voltage in a low responsetime appearing after a given time has passed when the gap is changedduring the lap welding or the butt welding and to carry out the pulseMAG arc welding method under correction of the arc length in accordancewith the variation in the gap.

A welding method described above is based on a pulse MAG arc weldingmethod to carry out the welding by using the pulse welding currentobtained by switching between the first pulse current group and thesecond pulse current group different from the first pulse current group.The consumable electrode is fed at a predetermined feed rate while eachvalue of pulse current value, pulse duty time, pulse frequency and basecurrent value of the first pulse current group is set to a value capableof forming a project transfer mode in which the molten metal graintransfers from the consumable electrode to the welding material in asynchronizing way to each of the pulse currents. The pulse currentvalue, pulse duty time, pulse frequency and base current of the secondpulse current group is set to a value different from that of the firstpulse current group within the range to hold the project transfer mode.Then, the arc length is periodically switched by energizing the pulsewelding current. When the arc length varies with the imbalance betweenthe wire feed rate and the wire melting speed, the arc length is rapidlyrecovered by changing quickly the pulse frequency, pulse duration, basecurrent value or pulse current value with the detected arc voltage. Atthe same time, the arc voltage varied with the variation in the gap isdetected. A pulse MAG arc welding method is completed after the arclength is provided with the correction corresponding to the gap bycontrolling the energizing ratio Ds between the first pulse duty timeand the second pulse duty time by the detected arc voltage.

Before the description of the welding method first the description isdirected to the welding method capable of recovering the arc length whenthe arc length is changed by the external disturbance. Next, thedescription will be directed to the welding method to make the arclength correction in accordance with the variation in the gap when thewelding material has the gap changed during the lap welding or the buttwelding.

Description of the recovery of changed arc length

First, the description will be directed to the effect to recover the arclength variation. In a pulse arc welding method switching between thefirst pulse current group and the second pulse current group, when thearc length varies with the unbalance between the wire feed rate and thewire melting speed, the arc voltage is quickly detected to compare thearc voltage detection signal Vd to the first arc voltage setting signalVs1 and to the second arc voltage setting signal Vs2. The pulsefrequency control signal Vf3 is changed in accordance with the signalCm2 obtained from the comparison among the above signals. In response tothe variation of the pulse frequency control signal Vf3, the pulsecurrent outputted from the welding electric source circuit PS varies inthe frequency and causes the wire melting speed to vary. As a result,the arc length variation can be recovered.

That is, when the arc voltage increases with the increase in the arclength, the decrease in the pulse frequency results in the increase inthe pulse period. Then, the wire melting speed becomes lower, and thearc length accordingly decreases to recover the original length. In areverse way, when the arc voltage decreases with the decrease in the arclength, the increase in the pulse frequency causes the pulse period tobe shorter and the wire melting speed to be higher. As a result, the arclength increases to recover the original length.

Description of the arc length correction corresponding to the variationin the gap of the butt joint.

With reference to FIGS. 58 (A) and (B) in addition to FIGS. 54 and 55 bywhich the description has been made with the variation in the arc lengthand the arc voltage with the variation in the gap of butt joint, thesecond effect of the welding method will be described.

The phenomenon occurring when the gap of butt joint is larger and thevariation in the arc voltage can be caused by the increase in the wireextension length to La+ΔL as shown in FIG. 54 (C). Therefore, the actualarc length is decreased from L0 to L3 and then the arc voltagedecreases. There is a time delay until the occurrence of the decrease inthe arc voltage. This time delay is corresponding to the switchingfrequency (1to 15 Hz) between the first pulse duty time T1 and thesecond pulse duty time T2. This switching period does not respond to thevariation in the arc voltage having a high variation speed similarly tothe arc variation due to the unbalance between the wire feed rate andthe wire melting speed but to the variation in the arc voltage generatedwith the decrease in the arc length caused by the decrease in the wiremelting speed due to the decrease in the pulse frequency.

Next, the description will be directed to the arc length correction whenthe arc voltage decreases with the variation in the gap.

As shown in FIG. 54 (C), when the arc voltage decreases with theincrease in the gap size, the detection signal to detect the decrease inthe arc voltage causes, for example, the second pulse duty time T2having the average value of pulse current in a large size to be longeror the first pulse current duty time T1 having a small average pulsecurrent to be shorter. Alternatively, T1 is made shorter while T2 ismade longer at the constant value of (T1+T2). As a result, it ispossible to increase the arc length with the increase in the wiremelting speed as shown in FIG. 58 (A). The wire extension length can bemade shorter from La to Lb at the time before the variation in the gap.Then, the actual arc length is L4 (L4≠L0). This causes the arc outsidediameter to be larger to A4 (A4≠A2) and the molten metal pool width tobe also larger to W4 (W4≠W2). Thus, the welding material 2 is meltedsufficiently at the both side of the gap. Therefore, the reinforcementis in a flat shape to prevent a generation of the welding defect.Further, the arc length correction and the flat shape of thereinforcement causes the arc length between the wire terminal 1a and thesurface 2a of the molten metal pool to be longer and prevents thecontact between the wire terminal 1a and the surface 2a of the moltenmetal pool and finally the generation of the arc cutting.

The phenomenon occurring when the gap of butt joint is smaller in areverse way and the arc voltage variation cause the actual arc length L5to be larger than L0 and the arc voltage to increase as shown in F55(C).

There is a time delay until the increase in the arc voltage which occurswith the operation where the arc flies to the outside of thereinforcement formed with the molten wire at the same arc length inspite of the smaller gap. This time delay responds to the switchingfrequency (0.5 to 15 Hz) between the first pulse duty time T1 and thesecond pulse duty time T2 and to the variation in the arc voltageresulting from the variation in gap.

Next, the description will be directed to the arc length correction whenthe arc voltage increases with the variation in the gap. When the actualarc length extends to the outside of the reinforcement due to thedecrease in the gap and causes the arc voltage to increase as shown inFIG. 55 (C), the detection signal to detect the decrease in the arcvoltage causes, for example, the second pulse duty time T2 having theaverage value of pulse current in a large size to be shorter or thefirst pulse current duty time T1 having a small average pulse current tobe longer. Alternatively, T1 is made longer while T2 is made shorter atthe constant value of (T1+T2). As a result, it is possible to decreasethe arc length with the decrease in the wire melting speed as shown inFIG. 58 (B). The wire extension length can be made longer from La at thetime before the variation in the gap to Lc. Then, the actual arc lengthis L7 (L7<L0). This causes the arc outside diameter to be shorter to A5(A5<A1) and the molten metal pool width to be also smaller to W5(W5<W1). Thus, the arc length is corrected into a short size with thedecrease in the gap size. It is possible to obtain the stable arc and toprevent the contact between the wire terminal 1a and the surface 2a ofthe molten metal pool and finally the generation of the arc cutting.

Description of arc length correction corresponding to the variation inthe gap of lap joint

FIGS. 59 (A) and (B) are structural model views illustrating the arclength correction when the gap of lap joint varies. The description withthe arc length correction with the variation in the gap of lap jointshown in FIGS. 59 (A) and (B) is the same as that of the arc lengthcorrection with the gap of the butt joint shown in FIGS. 58 (A) and (B)by exchanging the word `butt plane` to `lap plane` and should beomitted.

Embodiment 23 . . . Description of butt welding shown in FIG. 50

FIG. 50 is a graph having the gap G mm of the butt at the welding lineplotted at a vertical axis and the welding speed WS cm/min plotted at ahorizontal axis and showing a range (shown by a oblique line) at whichthere is no melt down and a capability of welding when the welding speedis changed between 30 and 100 cm/min and the gap is also changed from1.5 to 6.5 mm in connection with a butt welding for an aluminum alloyA5052 plate of 1.5 mm thickness.

In FIG. 50, the welding condition is that the welding current averagevalue is 100 to 175 A, and arc voltage is 17.5 to 21 V. The first pulsecurrent group of the pulse current value 280 A having the pulse duration1.2 msec and the second pulse current group of the pulse current value380 A of the pulse duration 1.2 ms are switched to each other with theswitching frequency 2.5 Hz.

In FIG. 50, a symbol a and a dotted line show the upper limit of the gapcapable of being welded when the welding is carried out with theenergizing ratio Ds held at the constant value of 0.5 according to thewelding method by claim 25. The gap of 3 mm is an upper limit which canbe welded at the low welding speed of 30 cm/min. With the welding speedhigher than 30 cm/min, the upper limit for the welding is lowered. Whenthe welding speed is higher than 70 cm/min, the upper limit for thewelding is decreased to 1.5 mm of the gap.

A pulse arc welding is carried out at the same condition as the aboveother than the energizing ratio Ds which is made variable from 0.3 to0.7 by an arc voltage detection signal. As shown by a open circle and asolid line, at the low welding speed of 30 cm/min, the limit size of thegap which can be welded is increased from 3 mm which is obtained withthe constant energizing ratio Ds to 6.5 mm according to the weldingmethod mentioned above. At the welding speed of 70 cm/min, the limitsize of the gap for welding is 1,5 mm with the constant energizing ratioDs but can be extended to 3.5 mm at a variable Ds.

The reason for making the limit size of gap for welding larger than thesize at the constant energizing ratio Ds is that the arc lengthcorrection is made by controlling the energizing ratio Ds by the arcvoltage detection signal as described in FIGS. 58 (A) and (B) with theproblem mentioned in FIGS. 54 (C) and 55 (D)

Embodiment 24 . . . Description of lap welding shown in FIG. 52

FIG. 52 is a graph having the gap G mm of the butt at the welding lineplotted at a vertical axis and the welding speed WS cm/min plotted at ahorizontal axis and showing a range (shown by a oblique line) at whichthere is no melt down and a capability of welding when the welding speedis changed between 30 and 100 cm/min and the gap is also changed from 2to 5 mm in connection with a lap welding for an aluminum alloy A5052plate of 1.5 mm thickness.

In FIG. 52, the welding condition is that the welding current averagevalue is 60 to 120 A, and arc voltage is 16.5 to 19 V. The first pulsecurrent group of the pulse current value 280 A having the pulse duration1.2 msec and the second pulse current group of the pulse current value380 A of the pulse duration 1.2 ms are switched to each other with theswitching frequency 2.5 Hz.

In FIG. 52, a symbol Δ and a dotted line show the upper limit of the gapcapable of being welded when the welding is carried out with theenergizing ratio Ds held at the constant value of 0.5 according to thewelding method by claim 26 The gap of 3 mm is an upper limit which canbe welded at the low welding speed of 30 to 50 cm/min. With the weldingspeed higher than the above value, the upper limit for the welding islowered. When the welding speed is higher than 60 cm/min, the upperlimit for the welding is decreased to 2 mm of the gap.

A pulse arc welding is carried out at the same condition as the aboveother than the energizing ratio Ds which is made variable from 0.3 to0.7 by an arc voltage detection signal. As shown by a open circle and asolid line, at the low welding speed of 30 to 60 cm/min, the limit sizeof the gap which can be welded is able to be increased from 3 mm whichis obtained with the constant energizing ratio Ds to 5 mm with thevariable Ds. At the gap of 5 mm , there is no partial melt down andcapability of welding. At welding speed of 100 cm/min, the limit size ofthe gap for welding can be extended from 2 mm with the constantenergizing ratio Ds to 3 mm at a variable Ds.

The reason for making the limit size of gap for welding larger than thesize at the constant energizing ratio Ds is that the arc lengthcorrection is made by controlling the energizing ratio Ds by the arcvoltage detection signal as described in FIGS. 59 (A) and (B) with theproblem mentioned in FIGS. 56 (C) and 57 (D).

A welding method includes the step of switching the wire feed rate WFbetween the first wire feed rate and the second wire feed rate with aswitching frequency F=0.5 to 5 Hz and to manage the ratio between thesecond welding current value I2 and the first welding current value I1to be 1.05 to 1.20. The following description will be directed to thecase in which the welding method including the switching step is appliedfor the butt welding and the lap welding as mentioned above.

The welding method including the switching step is to give a shapecorrection to the reinforcement by switching the wire feed rate with thecontrolled energizing ratio Ds in addition to the effect to give the arclength correction corresponding to the gap by controlling the energizingratio Ds.

In a welding method as mentioned above, the detection signal detects thedecrease in the arc voltage with the increase in the gap and makes thearc length correction by managing the energizing ratio Ds to increasethe arc length. As a result, it has bee possible to extend the limitsize of the gap for welding much larger than the size with the constantenergizing Ds.

For the butt welding and lap welding method it is possible to extend therange at which there is no melt down by giving the arc length acorrection when the gap is larger. However, with the increase in the gapsize, the lack of the molten metal causes the reinforcement to be low inthe building-up height and in a flat appearance of the bead.

In the welding method the detection signal detects the decrease in thearc voltage with the large variation in the gap size and makes the arclength correction by managing the energizing ratio Ds to increase thearc length. At the same time, the wire feed rate is increased inaccordance with the energizing ratio Ds to increase the welding currentas well as the molten metal amount. The molten metal fills the enlargedgap without the lack and builds up the reinforcement having a beautifulappearance of bead.

In a reverse way, in the welding method the detection signal detects theincrease in the arc voltage with the decrease in the gap size and makesthe arc length correction by managing the energizing ratio Ds todecrease the arc length. It is possible to make the limit size of thegap for welding larger than the size at the constant energizing ratio Dsas shown in the embodiment 23.

In the butt welding and lap welding method the arc length correction tomake the arc length shorter with the decrease in the gap size can extendthe range at which the welding can be carried out. However, with thedecrease in gap size, the molten metal in a too much amount makes thereinforcement to be too high in the build up height.

In the welding method the detection signal detects the increase in thearc voltage with the decrease in the gap size and makes the arc lengthcorrection by managing the energizing ratio Ds to decrease the arclength. The wire feed rate is decreased in accordance with the switchedenergizing ratio Ds so that the welding current as well as the moltenmetal amount decreases. It is possible to prevent the contact betweenthe wire terminal and the surface of the molten metal resulting in thearc cutting even with the arc length set to a short size by decreasingthe height of the reinforcement.

Comparison of the wire feed rate at the butt welding between theconstant value and the switching value

                  TABLE 2                                                         ______________________________________                                        constant feed                                                                 rate            feed rate switching                                           average value of                                                                              welding current                                                                          welding current                                    welding current of first pulse                                                                           of second pulse                                    Ia (A)          M1 (A)     M2 (A)                                             ______________________________________                                        a     100           100        120                                            b     110           110        130                                            c     130           130        155                                            d     150           150        175                                            ______________________________________                                    

In a welding method shown in FIG. 50, Table 2 indicates the averagevalue of welding current Ia at the points a to d on a solid curve inconnection with the welding method in a constant value of the wire feedrate and average value of the welding current M1 of the first pulse dutytime T1 and the average value of the welding current M2 of the secondpulse duty time T2 at points a to d on the solid curve in connectionwith the welding method having the wire feed rate switched.

FIG. 60 is a sectional view of the beads obtained at points a to d on asolid line when the welding method according to FIG. 50 is carried outat a constant wire feed rate and the beads obtained at points a to d ona solid line when the welding method according to FIG. 50 is carried outat switched wire feed rate.

With the comparison between the sectional views of the beads obtained bythe different two ways, it is clear that the bead obtained at theconstant wire feed rate has the insufficient reinforcement, whereas thebead obtained at the switched wire feed rate has the sufficientreinforcement produced with the increased wire molten amount resultedfrom the increase in the welding current value higher by 10 to 20% thanthe usual average value of the welding current.

Comparison between the lap welding methods at a constant wire feed rateand switched wire feed rate

                  TABLE 3                                                         ______________________________________                                        constant feed                                                                 rate            feed rate switching                                           average value of                                                                              welding current                                                                          welding current                                    welding current of first pulse                                                                           of second pulse                                    Ia (A)          M1 (A)     M2 (A)                                             ______________________________________                                        a     60            60          70                                            b     70            70          85                                            c     85            85         100                                            d     100           100        120                                            ______________________________________                                    

In a welding method shown in FIG. 52, Table 3 indicates the averagevalue of welding current Ia at the points a to d on a solid curve inconnection with the welding method in a constant value of the wire feedrate and average value of the welding current M1 of the first pulse dutytime T1 and the average value of the welding current M2 of the secondpulse duty time T2 at points a to d on the solid curve in connectionwith the welding method having the wire feed rate switched.

FIG. 61 is a sectional view of the beads obtained at points a to d on asolid line when the welding method according to FIG. 52 is carried outat a constant wire feed rate and the beads obtained at points a to d ona solid line when the welding method according to FIG. 50 is carried outat switched wire feed rate.

With the comparison between the sectional views of the beads obtained bythe different two ways, it is clear that the bead obtained at theconstant wire feed rate has the insufficient reinforcement whereas thebead obtained at the switched wire feed rate has the sufficientreinforcement produced with the increased wire molten amount resultedfrom the increase in the welding current value higher by 10 to 20% thanthe usual average value of the welding current.

Description of FIGS. 62 to 64

FIG. 62 is a graph showing a cracking test result using the testspecimen to be described in FIG. 64 and having a cracking ratio(LC/LW)×100% plotted at the vertical axis and a switching frequency ofpulse current plotted at the horizontal axis. A reference character LCdenotes the cracking length (mm) and a character reference LW denotes awelding length (mm). It is clear from FIG. 62 that the cracking ratio isminimum at the switching frequency of 4 Hz.

FIG. 63 is a graph showing the relationship between the switchingfrequency and the average grain size of the welded metal subjected tothe same welding condition as that of FIG. 62. It is clear from FIG. 63that the average grain size is minimum at the switching frequency ofabout 4 Hz. Accordingly, it is clear that the decrease in the averagegrain size of the welded metal results in the decrease in the crackingratio.

FIG. 64 is a structural model view illustrating the comparison betweenthe beads obtained with the conventional pulse MIG arc welding methodand with the pulse MIG arc welding method for changing the arc length toobtain the fine grain size according to the present invention. Thewelding length is achieved at the half by the conventional pulse MIG arcwelding method and at another half achieved subsequentially by the MIGarc welding method according to claim of the present invention. Theconventional pulse MIG arc welding method generates the cracks over allthe welding length. The welding method according to the claim of thepresent invention is carried out subsequently to the conventionalwelding method and does not generate the crack after the delay time atwhich a slight crack is generated. This confirms the effect of the claimof the present invention.

Description of FIGS. 65 and 67

FIG. 65 is a graph showing the relationship between the variation valueof the arc length Le mm (horizontal axis) and a molten metal poolvibration width PW mm (vertical axis). The welding condition is that thepulse current is switched by the switching frequency 4 Hz. As shown inFIG. 65, the increase in the variation value Le causes the increase inthe molten metal pool vibration width PW.

FIG. 66 is a graph showing the relationship between the arc lengthvariation value Le mm (horizontal axis) and the average grain size SDmicro millimeter (vertical axis). The welding condition is that thepulse current is switched by a switching frequency 4 Hz. It is clearfrom FIG. 66 that the average grain size becomes larger than 200 micronmillimeter when the arc length variation Le is less than 1 mm. Since thecracking is easily generated at the average grain size higher than 200micron millimeter, the arc length variation value Le is required to behigher than one mm.

FIG. 67 is a graph showing the relationship between the switchingfrequency F Hz (horizontal axis) and the arc length variation value Lemm (vertical axis). From FIG. 66, it is clear that the arc lengthvariation value Le is required to be higher than 1 mm in order to makethe average grain size SD to be less than 200 micron millimeter. Inorder to achieve this requirement, FIG. 67 indicates that the switchingfrequency F is required to be less than 15 Hz. It is difficult for themelt length at the wire extension length to follow the switchingfrequency F at the switching frequency F higher than 15 Hz. On the otherhand, it is clear from FIG.63 that the average grain size SD less than200 micron millimeter can be achieved by the switching frequency Fhigher than 0.5 Hz. As a conclusion, in the welding method according tothe claim of the present invention, it is necessary that the arc lengthvariation value Le is less than 1 mm and the switching frequency F is0.5 to 15 Hz.

The welding method is to prevent the generation of the cracking and toimprove the accuracy in the non-destructive test by stirring thestainless steel molten pool in order to obtain the fine grain size.

Description of FIG. 68

FIG. 68 (A) is a perspective view of the bead obtained when a stainlesssteel of 4 mm thickness is welded at the average value of the weldingcurrent 100 A and a pulse current of average arc voltage of 19 V at awelding speed of 30 cm/min with stainless wire of 1.0 mm diameter by thepulse MIG arc welding method to generate the variation value of the arclength Le in accordance with the above welding method FIG. 68 (B) and(C) are graph showing the variation in the vibration width PW and theheight PN of the molten metal pool with time, respectively.

The bead obtained with the above welding condition shows a wave patternof solidified metal as shown in FIG. 68 (A). The vibration of the moltenmetal pool under welding according to the present claim is photographedby a high speed video camera and analyzed with the video analyzingapparatus. The vibration width PW is 1.0 mm as shown in FIG. 68 (B). Itis clear from FIG. 68 (C) that the convection in the molten metal poolis sufficiently carried out from the surface to the inside to producefine grain boundaries in the solidified metal having columnar crystal.Since the cracking due to the solidification usually moves along withthe grain boundaries, the fine grain boundaries causes the cracking tomove with difficulty. The cracking is filled with the molten metal in anaccelerated way due to the molten metal vibration induced by thecracking itself (referred to healing phenomenon in the weldingsolidification metallurgy) when the vibration in the molten metal islarge. In view of this point, the large vibration is useful for theprevention of the cracking.

Embodiment . . . Description of FIG. 69

FIG. 69 (A) is a perspective view of the bead after the radiographictest on the welding bead obtained with the welded stainless steel18Cr8Ni subjected to conventional MIG welding method. In can be seenthat the welding bead shows a black shadow at the positions df1, df2 anddf3 along with the grain boundary of large crystals. These black shadowcan be seen in the bead when the cracking generates at the weldingmetal. It is difficult to determine whether the black shadow is due tothe cracking or not.

FIG. 69 (B) is a perspective view of the bead after the radiographictest on the welding bead with the stainless steel 18Cr8Ni subjected tothe MIG arc welding method according to the present claim. Thedisturbance of the molten metal pool due to the periodic variation inthe arc length causes the grain size to decrease. Accordingly, the blackshadow shown in FIG. 69 (A) can not be seen. It is concluded that thepulse MIG arc welding method according to the present invention causesthe grain size of welded stainless steel to be small and prevents thegeneration of the cracking. The radiographic test does not produce theblack shadow which may suggest the possible cracking.

Description of FIG. 70

FIG. 70 (A) is a graph showing a echo figure of the ultrasonic test onthe 18-8 stainless steel subjected to the conventional MIG weldingmethod. It is seen from FIG. 70 (A) that the sample having no defect dueto the welding shows various peaks nf11 whereas the sample having thedefect prepared in advance to the test shows the various peaks nf12 addf11. The peak df11 seems to be corresponding to the defect but thepeaks nf12 has no reason to appear and makes the ultrasonic testuncertain. The detection accuracy for the defect is very low.

On the other hand, FIG. 70 (B) is a graph showing an echo figure of theultrasonic test on the 18-8 stainless steel subjected to the pulse MIGarc welding method described above. It is seen from FIG. 70 (B) that thesample having no defect shows an echo figure showing a slight peak nf21whereas the sample having a defect prepared in advance to the test showsa peak df21 corresponding clearly to the defect and a slight peak nf22.The slight peak nf21 and nf22 may be resulted from the fine grain sizeand are apparently different from the large peak df21 in the height.Therefore, the defect due to the welding can be clearly detected by theradiographic test in connection with the pulse MIG arc welding method.

Description of FIG. 71

FIG. 71 is a graph showing the relationship between the level range I toV for the echo height EH detected in accordance with the JIS (JapaneseIndustrial Standard) Z3060 (vertical axis) and the average grain size SDmicro millimeter (horizontal axis). The range III is a standard of echoheight for determining the class in accordance with JIS Z3060. The echoheight higher than that of the range III appears at a grain size largerthan 300 micro millimeter. When the average grain size is higher than250 micron millimeter, the bead has the a long stray crystal generatedat the center thereof. The radiographic test on such a sample detects ablack shadow df1 to df3 along with the stray crystal and decreases thedetection accuracy on the defect.

Description of FIG. 72

FIG. 72 is a graph showing the relationship between the switchingfrequency F Hz (horizontal axis) and the average grain size micronmillimeter in connection with the welding condition the same as that ofFIG. 71. It is clear from FIG. 72 that the switching frequency of 4 Hzshows the minimum grain size while the frequency range lower than 1 Hzor more than 15 Hz generates the average grain size more than 300 micronmillimeter. The average grain size more than 300 micron millimetercauses the non-destructive test such as radiographic test and theultrasonic test to decrease the accuracy.

Description of FIG. 73

FIG. 73 is a graph showing the relationship between the variation valueof the arc length Le mm (horizontal axis) and the vibration width ofmolten metal pool PW mm (vertical axis). The welding is carried out byswitching the pulse current with the switching frequency 4 Hz. As shownin FIG. 73, an increase in the variation value of the arc length Leresults in the increase in the vibration width of the molten metal pool.

Description of FIG. 74

FIG. 74 is a graph showing the relationship between the variation valueof the arc length Le mm (horizontal axis) and the average grain sizemicro millimeter (vertical axis). The welding is carried out byswitching the pulse current with the switching frequency 4 Hz. As shownin FIG. 73, an increase in the variation value of the arc length Leresults in the decrease in the average grain size due to the increaseddisturbance of the molten metal pool. The variation value in the arclength Le is less than 1 micron millimeter shows the average grain sizehigher than 250 micron millimeter. The average grain size higher than300 micron millimeter causes the non-destructive test to decrease in theaccuracy and also generates more frequently the cracking. Therefore, itis necessary for the grain size more than to 300 micron millimeterobtain the variation value in the arc length more than 1 micronmillimeter.

Description of FIG. 75

FIG. 75 is a graph showing the relationship between the switchingfrequency Hz (horizontal axis) and the variation in the arc length Le mm(vertical axis). As shown in FIG. 74, it is necessary for the grain sizemore than 300 micron millimeter to obtain the variation value in the arclength more than 1 micron millimeter. As a result, the switchingfrequency must be lower than 15 Hz. With the switching frequency morethan 15 Hz, it is difficult for the variation in the extension length atthe terminal of the molten metal to follow the switching frequency. Insuch a way, the average grain size SD lower than 250 micron millimeterrequires the frequency more than 1 Hz as mentioned with FIG. 72. Hence,it is necessary to keep the switching frequency within 1 to 15 Hz andthe variation value in the arc length more than 1 mm.

Description of FIG. 76

FIG. 76 is a graph showing the relationship between the variation valuein the arc voltage ΔVa V (horizontal axis) and the variation value ofthe arc length Le mm (vertical axis) at the MIG arc welding withoutpulse. The welding condition is; the welding electric current=200 A, thefirst arc voltage=23 V and the arc length Feibush mm at the firstwelding condition with a given constant rate of feeding of stainlesssteel SUS 308 of 1.0 mm diameter. The relation between the variationvalue in the arc voltage ΔVa V and the variation value in the arc lengthLe at the second welding condition is shown by a dotted line and Δsymbol. The stainless steel SUS 308 in a diameter of 1.2 mm is fed at agiven constant rate. The first welding condition is; the weldingcurrent=250 A, the first arc voltage=25 V and the arc length Feibush mm.The relation between the variation in the arc voltage ΔVa V and thevariation value in the arc length Le at the second welding condition isshown by a solid line and a open circle. The arc length is changedwithin the spray transfer range since the first and the second weldingconditions are provided with the welding current higher than thecritical value Ic.

Description of FIG. 77

FIG. 77 is a graph showing the relationship between the switchingfrequency F Hz (horizontal axis) and the average grain size SD micronmillimeter (vertical axis) at the MIG arc welding without pulse. Thewelding condition is that the welding electric current=200 A, the firstarc voltage=23 V and the arc length Feibush mm at the first weldingcondition with a given constant rate of feeding of stainless steel SUS308 of 1.0 mm diameter. The second welding condition is in an arcvoltage of 26 V. It is clear from FIG. 77 that the switching frequencyof 4 Hz shows the minimum grain size while the frequency range lowerthan 1 Hz or more than 15 Hz generates the average grain size more than300 micron millimeter in a similar way to that of FIG. 72. The averagegrain size more than 300 micron millimeter causes the non-destructivetest such as radiographic test and the ultrasonic test to decrease theaccuracy.

The welding method also prevents the generation of porosity by stirringthe molten aluminum pool under the welding condition that the switchingfrequency is 0.5 to 25 Hz and the variation in the arc length Le is morethan 1 mm.

Description of FIG. 78

FIG. 78 is a graph showing the relationship between the molten metalpool width Pw mm (horizontal axis )and a number of porosity (pieces/50mm ) at the welding length of 50 mm (vertical axis) with the weldinghaving the pulse current to flow. It is clear from FIG. 78 that themolten metal pool width PW lower than 0.5 mm shows a rapid increase inthe porosity. The decrease in the porosity requires the molten metalpool width larger than 0.5 mm . The welding condition for the data inFIG. 78 is that aluminum plate is welded in an argon gas includingintentionally 0.1% of hydrogen by using aluminum wire of 1.6 mm diameterfor a purpose to determine the number of porosity.

At this time the first pulse current group P1 is that the first pulsecurrent IP1=280 A, the first pulse duration TP1=1.2 ms, the first basecurrent value IB1=30 A, the pulse frequency=about 100 Hz. The secondpulse current group P2 is in a condition; the second pulse currentvalue=300 A, the second pulse duration TP=2.0 ms, the second basecurrent value IB2=30 A and the pulse frequency=70 Hz. The first pulsecurrent group P1 and the second pulse current group P2 are switchedperiodically to each other at the switching frequency 4 Hz. At the pulsecurrent duty time, the first arc voltage value Va1 and the second arcvoltage Va2 are 17.5 V and 20 V, respectively, and the arc lengthvariation value Le is 3.5 mm.

Description of FIGS. 79 to 81

FIG. 79 is a graph showing the relationship between the switchingfrequency F Hz (horizontal axis) and the molten metal pool width PW mm(vertical axis) with the welding energized by the pulse current. It isseen from FIG. 79 that the molten metal pool width higher than 0.5 mmrequires the switching frequency F Hz lower than 25 Hz.

FIG. 80 is a graph showing the relationship between the switchingfrequency F Hz (horizontal axis) and the number of porosity (verticalaxis) at the welding length of 50 mm BN (pieces/50 mm ) when the weldingis carried out at the same condition as that of FIG. 79. As shown inFIG. 80, the number of porosity increases rapidly with the switchingfrequency lower than 0.5 Hz or higher than 25 Hz. A small number ofporosity can be obtained by keeping the switching frequency between 0.5and 25 Hz. The switching frequency lower than 0.5 Hz can not vibrate themolten metal pool. On the other hand, the switching frequency higherthan 25 Hz causes the variation in the molten metal length at theterminal of the wire extension length not to follow the frequency F.

FIG. 81 is a graph showing the relationship between the number of theporosity at the welding length of 10 mm m BN (pieces/10 mm m) (verticalaxis) and the variation in the arc length Le mm (horizontal axis) whenaluminum alloy A5052 plate in a thickness of 3 mm is welded withaluminum alloy wire in a diameter of 1.2 mm. At this time, the conditionis in the following; the average value of the welding current Ia=100 A,the average value of the arc voltage Va=19 V and the switchingfrequency=0.5 to 2 Hz. It is clear from FIG. 81 that the variation valueof the arc length Le more than 5 mm causes a rapid increase in thenumber of the porosity. This comes from the following the reason: Inconnection with the gas sealed nozzle 5 commercially available, the arclength is set to a short size of 3 mm for the purpose of preventing theshort circuit. The variation value in the arc length more than 5 mmresults in the arc length more than 8 mm. The terminal 1a of the wirereaches the vicinity of the gas sealed nozzle and disturbs the gassealed atmosphere. The insufficient gas sealed atmosphere causes thegeneration of the porosity. Therefore, it is suitable to keep thevariation in the arc length Le lower than 5 mm.

FIG.82 is a graph showing the relation between the switching frequency FHz necessary for obtaining the vibration width of the molten metal poolmore than 0.5 mm (horizontal axis) and the variation value of arc lengthLe (vertical axis). It is seen that the molten metal pool vibrationwidth more than 0.5 mm can be obtained at the range upper the curve bythe welding method according to claim 29. At the range of switchingfrequency F=0.5 to F=12 Hz, the variation in the arc length Le isrequired to be more than 1 mm and at the range of switching frequencyF=25 Hz, the variation in the arc length Le is required to be more than0.5 mm. It is necessary that the variation value in the arc length Le ismore than 0.5 mm and is less than 5 mm in accordance with thedescription in FIG. 81. The arc welding method accordingly requires theswitching frequency to be 0.5 to 25 Hz. It is necessary to keep thevariation value in the arc length Le in a range more than 0.5 mm andless than 5 mm in accordance with the increase in the switchingfrequency.

In FIG. 82, the variation value in the arc length Le necessary forobtaining the molten metal pool width more than 0.5 mm is 1 mm at arange of switching frequency F less than 12 Hz and then is smaller withthe increase in the switching frequency. However it is possible toobtain the molten metal pool width more than 0.5 mm at the increasedfrequency range. This may be resulted from the following reason: Withreference to FIG. 81, the welding condition is set to the following; theaverage value of the welding current Ia=100 A, the average value of thewelding voltage Va=19 V and welding speed WS=40 cm/min. As a results,the molten metal pool diameter is about 1 cm. The relationship betweenthe molten metal pool diameter and the resonance frequency of the metalFr can be expressed by the following equation 1:

    Fr=(surface tension/density×diameter of molten metal pool).sup.1/2

Aluminum has a surface tension of 900 dyn/cm and density of 2.5 g/cc.The Fr can be calculated from the equation 1 for the molten metal pooldiameter of 1 cm, Fr=19 Hz This is a resonance frequency of the moltenaluminum pool. When the switching frequency is equivalent to this Fr, aslight variation value in the arc length Le permits the molten aluminumpool to vibrate in a considerably large degree.

As a practical matter, the usual MIG welding method can produce theresonance frequency of molten metal pool of about 10 to 25 Hz. Hence,the switching frequency of 10 to 25 Hz permits the molten metal pool tovibrate easily. However, it is necessary to change forcedly the arclength in a large degree for the purpose of vibrating the molten metalpool with the switching frequency other than 10 to 25 Hz. The switchingfrequency less than 10 Hz permits the arc length to vary easily in alarge degree. However, at the switching frequency higher than 25 Hz, itis necessary for the vibration of the molten metal pool to obtain thelarge variation value in the arc length Le. As a practical matter, thevariation in the molten metal length at the wire extension length cannot follow the switching frequency. Therefore, it is concluded that thesuitable switching frequency is 0.5 to 25 Hz.

Welding apparatus according to the present invention

The general structure of the welding apparatus is based on a pulse MAGwelding apparatus capable of switching between the first pulse currentgroup to obtain the first arc length Lt and the second current group toobtain the second arc length Left and right with a switching signalaccording to the present invention.

The welding apparatus of the present invention comprises the followingfunctions: An arc voltage control circuit comprises the arc voltagedetection circuit VD for outputting the arc voltage detection signal Vdupon detecting the arc voltage, and a comparator CM2 outputting an arcvoltage control signal Cm2 from the difference between the arc voltagedetection signal Vd and the arc voltage switching signal S6 obtained byswitching between the arc voltage setting signal Vs1 and the second arcvoltage setting signal Vs2 or the first arc voltage setting signal Vs1.

A pulse base current control circuit outputs the pulse base currentcontrol signal controlling the pulse frequency f3 corresponding to thearc voltage control signal Cm2, the pulse duration TP3, the base currentvalue IB3 or the pulse current value IP3.

A first pulse base current setting circuit outputs the first pulse basecurrent setting signal setting three conditions excluding the conditionto control with the pulse base current control signal among the fourconditions of the pulse current value, pulse duration, the pulsefrequency and the base current of the first pulse current group. Asecond pulse base current setting circuit outputs the second pulse basecurrent setting signal setting three conditions excluding the conditionto control with the pulse base current control signal among the fourconditions of the pulse current value, pulse duration, the pulsefrequency and the base current of the second pulse current group.

A switching circuit HL outputs the switching signal H2 under switchingwith the switching frequency f=0.5 to 25 Hz.

A plurality of switching setting circuit outputs the arc voltageswitching signal S6 obtained by switching the first arc voltage settingsignal Vs1 and the second arc voltage setting signal Vs2 with aswitching signal H1, a switching setting signal obtained by switchingthe first pulse base current setting signal and the second pulse basecurrent setting signal with a switching signal H1 or both of thesesignals. A pulse control signal generator outputs the first pulsecontrol signal Pf1 and the second pulse control signal Pf2 uponreceiving the pulse base current control signal and the switchingsetting signal. A welding power control circuit outputs the first pulsecurrent group upon receiving the first pulse control signal Pf1 and thesecond pulse control signal Pf2 upon receiving the second pulse controlsignal Pf2.

Described hereinbelow are three cases of the present invention when thearc voltage is controlled by the pulse frequency. A pulse base currentcontrol circuit for outputting the pulse base control signal comprises apulse frequency control signal generator Vf3 for outputting a pulsefrequency control signal controlling the pulse frequency f3. The firstpulse current setting circuit for outputting the first pulse basecurrent setting signal comprises the pulse current setting circuit IP1for setting the pulse current value setting signal Ip1, the pulseduration setting circuit TP1 for setting the pulse duration settingsignal Tp1, and a base current setting circuit IB1 for setting the basecurrent setting signal Ib1.

The welding apparatus according to a first embodiment is a pulse MAGwelding apparatus comprising the following functions: A second pulsebase current setting circuit for outputting the second pulse basecurrent setting signal comprises a second pulse current value settingcircuit IP2 for setting the second pulse current value setting signalIp2, a pulse duration setting circuit TP1 for setting a pulse durationsetting signal Tp1 and a base current setting circuit IB1 for setting abase current setting signal Ib1.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current value switching circuit SW1 for outputting aswitching pulse current value signal S1 obtained by switching betweenthe pulse current value setting signal Ip1 and the second pulse currentsetting signal Ip2. A pulse control signal generator for receiving pulsebase current control signal and the switching setting signal comprises apulse frequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df3 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and a base pulse current switching circuit SW5 for switching between thepulse current value switching signal S1 and the base current settingsignal Ib1 with the pulse duration frequency signal Df3.

Description of FIG. 83

FIG. 83 is a block diagram of the first embodiment of the welding methodhaving the welding waveform shown in FIG. 92 of the present invention.

In FIG. 83, a welding power control circuit PS having the power suppliedfrom the commercial AC electric supplier supplies the power between apower supplying tip 4 of a consumable electrode 1 and a welding material2, and generates an arc 3. The consumable electrode 1 is fed by a wirefeeding roller Wr rotated with a wire feeding motor WM. A wire feedingrate control circuit WC receives a wire feeding rate control signal Cm1from a wire feeding rate comparing circuit (the first comparison circuithereinafter) to compare a signal Im described later with a feeding ratedetection signal Wd of a wire feeding rate detection circuit WD of awire feeding motor WM and sends a wire feeding motor WM a wire feedingrate control signal Wc. The arc voltage setting circuit VS1 is to setthe arc voltage and outputs an arc voltage setting signal Vs1. A secondcaparison circuit CM2 outputs an arc voltage control signal Cm2 from thedifference between the arc voltage setting signal Vs1 and the arcvoltage detection signal Vd of the arc voltage detection circuit VD. Aduty frequency setting circuit FT is to set a switching frequency F of aswitching signal H1 to switch between the first pulse duty time T1 andthe second pulse duty Time T2, and outputs a duty frequency signal Ftwhich is suitably in a range from 0.5 to 25 Hz. The welding speed is ina close relation with the switching frequency F to obtain a suitablewelding result. The switching circuit HL receives a duty frequencysignal F corresponding to the welding speed after the duty frequencysetting circuit Ft receives the welding speed setting signal Ws of thewelding speed setting circuit WS. A duty ratio setting circuit DT is toset a ratio of the second pulse duty time T2 at the second weldingcondition to the first pulse duty time T1 at the first welding conditionand outputs a duty ratio signal Dt. The switching signal generator HLoutputs a switching signal H1 to switch periodically between the firstpulse duty time T1 and the second pulse duty time T2 upon receiving thesignal Ft and the signal Dr. The first pulse current value settingcircuit IP1 and the second pulse current value setting circuit IP2output the first pulse current value setting signal Ip1 and the secondpulse current value setting signal Ip2, respectively. The circuit SW1outputs a pulse current switching signal S1 obtained by switchingbetween the signals Ip1 and Ip2 with a switching signal H1.

A pulse frequency signal VF3 outputs a pulse frequency control signalVf3 in accordance with the arc voltage control signal Cm2. The pulseduration frequency control signal generator DF3 outputs a pulse durationfrequency control signal Df3 consisting of a pulse duration settingsignal Tp1 and the pulse frequency control signal Vf3. A pulse basecurrent switching circuit SW5 outputs a pulse control signal Pf1obtained by switching, with a pulse duration frequency control signalDf3, between a pulse current switching signal Ip1 of the first weldingcondition and a base current setting signal Ib1 at the first weldingcondition, and a pulse control signal Pf2 obtained by switching, with apulse duration frequency control signal Df3, between a pulse currentswitching signal Ip2 of the second welding condition and a base currentsetting signal Ib1 at the second welding condition. Both signals Pf1 andPf2 are inputted to the welding power control circuit PS.

Description of FIG. 92

In FIG. 92, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP1, a firstpulse duration TP1, a first pulse frequency f3 and a first base currentIB1. Reference characters P2, P2 . . . . P2 denote a second pulsecurrent group consisting of a second pulse current value IP2, a secondpulse duration TP1 the same as the first pulse duration, a second pulsefrequency f3 the same as the first pulse frequency and a second basecurrent IB1 the same as the first base current. The first pulse dutytime T1 and the second pulse duty time Y2 are switched to each otherwith the switching signal H1 at a switching period T1+T2 of a lowfrequency of, for example, 0.5 to 25 Hz.

Reference characters M1 and M2 denote the average value of the weldingcurrent at the first and the second pulse duty times T1 and T2,respectively, reference character Ia denotes an average value of thewelding current.

The welding apparatus according to a second embodiment is a pulse MAGwelding apparatus comprising the following functions: A second pulsebase current setting circuit for outputting the second pulse basecurrent setting signal comprises a pulse current value setting circuitIP1 for setting the pulse current value setting signal Ip1, a secondpulse duration setting circuit TP2 for setting a second pulse durationsetting signal Tp2 and a base current setting circuit IB1 for setting abase current setting signal Ib1.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current value switching circuit SW2 for outputting apulse duration switching signal S2 obtained by switching between thepulse duration setting signal Tp1 and the second pulse duration settingsignal Tp2. A pulse control signal generator for receiving pulse basecurrent control signal and the switching setting signal comprises apulse frequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df31 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and the second pulse duration frequency signal Df32 consisting of thepulse frequency signal Vf3 and the second pulse duration signal Tp2 anda base pulse current switching circuit SW5 for switching between thepulse current value setting signal IP1 and the base current settingsignal Ib1 with the second pulse duration frequency signal Df32.

FIG. 84 is a block diagram of the second embodiment of the weldingmethod having the welding waveform shown in FIG. 93.

In FIG. 84, the structures the same as those of FIG. 83 are denoted withthe same characters the same as those of FIG. 83 and are omitted in thedescription. Only different points are described hereinbelow.

The first pulse duration setting circuit TP1 and the second pulseduration setting circuit TP2 output the first pulse duration settingsignal Tp1 and the second pulse current duration setting signal Tp2,respectively. The circuit SW2 outputs a pulse duration switching signalS2 obtained by switching between the signals Tp1 and Tp2 with aswitching signal H1.

A pulse frequency signal circuit VF3 outputs a pulse frequency controlsignal Vf3 in accordance with the arc voltage control signal Cm2. Thepulse duration frequency control signal generator DF3 outputs a pulseduration frequency control signal Df31 consisting of a pulse durationsetting signal Tp1 and the pulse frequency control signal Vf3 inaccordance with the first welding condition and a second pulse durationfrequency control signal Df32 consisting of a second pulse durationsetting signal Tp2 and the pulse frequency control signal Vf3 inaccordance with the second welding condition. A pulse base currentswitching circuit SW5 outputs a pulse control signal Pf1 obtained byswitching, with a pulse duration frequency control signal Df3, between apulse current switching signal Ip1 of the first welding condition and abase current setting signal Ib1 at the first welding condition, and apulse control signal Pf2 obtained by switching, with a pulse durationfrequency control signal Df3, between a pulse current switching signalIp2 of the second welding condition and a base current setting signalIb1 at the second welding condition. Both signals Pf1 and Pf2 areinputted to the welding power control circuit PS.

Description of FIG. 93

In FIG. 92, reference characters P2, P2, . . . P2 denote a second pulsecurrent group consisting of a second pulse current value IP1 the same asthe first pulse current value, a second pulse duration TP2, a secondpulse frequency f3 the same as the first pulse frequency and a secondbase current IB1 the same as the first base current. Others are the sameas those of FIG. 92 and should be omitted.

The welding apparatus according to a third embodiment is a pulse MAGwelding apparatus comprising the following functions: A second pulsebase current setting circuit for outputting the second pulse basecurrent setting signal comprises a pulse current value setting circuitIP1 for setting the pulse current value setting signal Ip1, a firstpulse duration setting circuit TP1 for setting a pulse duration settingsignal Tp1 and a second base current setting circuit IB2 for setting asecond base current setting signal Ib2.

A switching setting circuit for outputting a switching setting signalcomprises a base current value switching circuit SW3 for outputting abase current switching signal S3 by switching between a first basecurrent setting signal Ib1 and the second base current setting signalIb2. A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df31 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and the pulse duration frequency signal Df3 consisting of the pulsefrequency signal Vf3 and the pulse duration signal Tp1 and a base pulsecurrent switching circuit SW5 for switching between the pulse currentvalue setting signal IP1 and the base current switching signal S3 withthe pulse duration frequency signal Df3.

Description of FIG. 85

FIG. 85 is a block diagram of the third embodiment of the welding methodhaving the welding waveform shown in FIG. 94.

In FIG. 85, the structures the same as those of FIG. 83 are denoted withthe same characters the same as those of FIG. 83 and are omitted in thedescription. Only different points are described hereinbelow.

The first base current setting circuit IB1 and the second base currentsetting circuit IB2 output the first base current setting signal Ib1 andthe second base current setting signal Ib2. The circuit SW3 outputs abase current switching signal S2 obtained by switching between thesignals Ib1 and Ib2 with a switching signal H1.

A pulse frequency signal VF3 outputs a pulse frequency control signalVf3 in accordance with the arc voltage control signal Cm2. The pulseduration frequency control signal generator DF3 outputs a pulse durationfrequency control signal Df3 consisting of a pulse duration settingsignal Tp1 and the pulse frequency control signal Vf3 in accordance withthe first welding condition. A pulse base current switching circuit SW5outputs a pulse control signal Pf1 obtained by switching, with a pulseduration frequency control signal Df3, between a pulse current switchingsignal Ip1 of the first welding condition and a base current settingsignal Ib1 at the first welding condition, and a pulse control signalPf2 obtained by switching, with a pulse duration frequency controlsignal Df3, between a pulse current switching signal Ip2 of the secondwelding condition and a base current setting signal Ib1 at the secondwelding condition. Both signals Pf1 and Pf2 are inputted to the weldingpower control circuit PS.

Description of FIG. 94

In FIG. 94, reference characters P2, P2, . . . P2 denote a second pulsecurrent group consisting of a second pulse current value IP1 the same asthe first pulse current value, a second pulse duration TP1 the same asthe first pulse duration, a second pulse frequency f3 the same as thefirst pulse frequency and a second base current IB2. Others are the sameas those of FIG. 92 and should be omitted.

The welding apparatus according to a fourth embodiment is a pulse MAGwelding apparatus comprising the following functions: A second pulsebase current setting circuit for outputting the second pulse basecurrent setting signal comprises a pulse current value setting circuitIP1 for setting the pulse current value setting signal Ip1, a secondpulse duration setting circuit TP2 for setting a second pulse durationsetting signal Tp2 and a base current setting circuit IB1 for setting afirst base current setting signal Ib1.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current value switching circuit SW1 for outputting apulse current switching signal S1 by switching between a first pulsecurrent setting signal Ip1 and the second pulse current setting signalIp2 and a pulse duration switching circuit SW2 for outputting a pulseduration switching signal S2 by switching between the first pulseduration setting signal Tp1 and the second pulse duration setting signalTp2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df31 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and the pulse duration frequency signal Df32 consisting of the pulsefrequency signal Vf3 and the pulse duration signal Tp2 and a base pulsecurrent switching circuit SW5 for switching between the pulse currentvalue switching signal S1 and the base current setting signal Ib1 withthe first pulse duration frequency signal Df31 and the second pulseduration frequency control signal Df32.

Description of FIG. 86

FIG. 86 is a block diagram of the forth embodiment of the welding methodhaving the welding waveform shown in FIG. 95.

In FIG. 86, the structures the same as those of FIG. 83 are denoted withthe same characters the same as those of FIG. 83 and are omitted in thedescription. Only different points are described.

A second pulse base current setting circuit for outputting the secondpulse base current setting signal comprises a pulse current valuesetting circuit IP1 for setting the pulse current value setting signalIp1, a second pulse duration setting circuit TP2 for setting a secondpulse duration setting signal Tp2 and a base current setting circuit IB1for setting a first base current setting signal Ib1.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current value switching circuit SW1 for outputting apulse current switching signal S1 by switching between a first pulsecurrent setting signal Ip1 and the second pulse current setting signalIp2 and a pulse duration switching circuit SW2 for outputting a pulseduration switching signal S2 by switching between the first pulseduration setting signal Tp1 and the second pulse duration setting signalTp2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df31 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and the pulse duration frequency signal Df32 consisting of the pulsefrequency signal Vf3 and the pulse duration signal Tp2 and a pulse basecurrent switching circuit SW5 outputs a pulse control signal Pf1obtained by switching, with a pulse duration frequency control signalDf3, between a pulse current switching signal Ip1 of the first weldingcondition and a base current setting signal Ib1 at the first weldingcondition, and a pulse control signal Pf2 obtained by switching, with apulse duration frequency control signal Df3, between a pulse currentswitching signal Ip2 of the second welding condition and a base currentsetting signal Ib1 at the second welding condition. Both signals Pf1 andPf2 are inputted to the welding power control circuit PS.

Description of FIG. 95

In FIG. 95, reference characters P2, P2, . . . P2 denote a second pulsecurrent group consisting of a second pulse current value IP2, a secondpulse duration TP2, a second pulse frequency f3 the same as the firstpulse frequency and a second base current IB1 the same as the first basecurrent. Others are the same as those of FIG. 92 and should be omitted.

The welding apparatus according to a fifth embodiment is a pulse MAGwelding apparatus comprising the following functions: A second pulsebase current setting circuit for outputting the second pulse basecurrent setting signal comprises a second pulse current value settingcircuit IP2 for setting the pulse current value setting signal Ip2, asecond pulse duration setting circuit TP2 for setting a second pulseduration setting signal Tp2 and a second base current setting circuitIB2 for setting a second base current setting signal Ib2.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current value switching circuit SW1 for outputting apulse current switching signal S1 by switching between a first pulsecurrent setting signal Ip1 and the second pulse current setting signalIp2 and a pulse duration switching circuit SW2 for outputting a pulseduration switching signal S2 by switching between the first pulseduration setting signal Tp1 and the second pulse duration setting signalTp2 and a base current switching circuit SW3 for outputting a basecurrent switching signal S3 obtained by switching the first base currentsetting signal Ib1 and the second base current setting signal Ib2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df31 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and the pulse duration frequency signal Df32 consisting of the pulsefrequency signal Vf3 and the pulse duration signal Tp2 and a base pulsecurrent switching circuit SW5 for switching between the pulse currentvalue switching signal S1 and the base current switching signal S3 withthe first pulse duration frequency signal Df31 and the second pulseduration frequency control signal Df32.

Description of FIG. 87

FIG. 87 is a block diagram of the fifth embodiment of the welding methodhaving the welding waveform shown in FIG. 96.

In FIG. 87, the structures the same as those of FIG. 83 are denoted withthe same characters the same as those of FIG. 83 and are omitted in thedescription. Only different points are described.

A second pulse base current setting circuit for outputting the secondpulse base current setting signal comprises a second pulse current valuesetting circuit IP2 for setting the pulse current value setting signalIp2, a second pulse duration setting circuit TP2 for setting a secondpulse duration setting signal Tp2 and a second base current settingcircuit IB2 for setting a second base current setting signal Ib2.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current value switching circuit SW1 for outputting apulse current switching signal S1 by switching between a first pulsecurrent setting signal Ip1 and the second pulse current setting signalIp2 and a pulse duration switching circuit SW2 for outputting a pulseduration switching signal S2 by switching between the first pulseduration setting signal Tp1 and the second pulse duration setting signalTp2 and a base current switching circuit SW3 for outputting a basecurrent switching signal S3 obtained by switching the first base currentsetting signal Ib1 and the second base current setting signal Ib2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df31 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and the pulse duration frequency signal Df32 consisting of the pulsefrequency signal Vf3 and the pulse duration signal Tp2 and a pulse basecurrent switching circuit SW5 outputs a pulse control signal Pf1obtained by switching, with a pulse duration frequency control signalDf3, between a pulse current switching signal Ip1 of the first weldingcondition and a base current setting signal Ib1 at the first weldingcondition, and a pulse control signal Pf2 obtained by switching, with apulse duration frequency control signal Df3, between a pulse currentswitching signal Ip2 of the second welding condition and a base currentsetting signal Ib1 at the second welding condition. Both signals Pf1 andPf2 are inputted to the welding power control circuit PS.

Description of FIG. 96

In FIG. 96, reference characters P2, P2, . . . P2 denote a second pulsecurrent group consisting of a second pulse current value IP2, a secondpulse duration TP2, a second pulse frequency f3 the same as the firstpulse frequency and a second base current IB2.

The description with reference to FIGS. 92 to 95 is directed to a casewhen the value of the second welding condition is larger than that ofthe first welding condition, that is, IP1<IP2, TP1<TP2, or IB1<IB2.However, the condition MI<M2 permits the value of the second weldingcondition lower than that of the first welding condition; that isIB1>IB2, when IP1<IP2, and TP1<TP2. Others are the same as the those inFIG. 92 and should be omitted.

The welding apparatus according to the second case when arc voltage iscontrolled by pulse frequency comprises the following functions: Asecond pulse base current setting circuit for outputting the secondpulse base current setting signal comprises a second arc voltage valuesetting circuit VS2 for setting the arc voltage value setting signalVs2, a pulse duration setting circuit TP1 for setting a pulse durationsetting signal Tp1, a base current setting circuit IB1 for setting abase current setting signal Ib1 and a pulse current value settingcircuit IP1 for outputting a pulse current value setting signal Ip1.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit SW6 for outputting an arcvoltage switching signal S1 by switching between a first arc voltagesetting signal Vs1 corresponding to the first arc length and the secondarc voltage setting signal Vs2 corresponding to the second arc length.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf31 corresponding to the arc voltage settingsignal Vs1 and the second pulse frequency control signal Vf32corresponding to the second arc voltage setting signal Vs1, a pulseduration frequency signal generator DF3 for outputting the first pulseduration frequency signal Df31 consisting of the first pulse frequencysignal Vf31 and the first pulse duration signal Tp1 and the pulseduration frequency signal Df32 consisting of the second pulse frequencysignal Vf32 and the pulse duration signal Tp1 and a base pulse currentswitching circuit SW5 for switching between the pulse current valuesetting signal Ip1 and the base current setting signal Ib1 with thefirst pulse duration frequency signal Df31 and the second pulse durationfrequency control signal Df32.

Description of FIG. 88

FIG. 88 is a block diagram of the embodiment of the welding methodhaving the welding waveform shown in FIG. 97.

In FIG. 88, the structures the same as those of FIG. 83 are denoted withthe characters the same as those of FIG. 83 and are omitted in thedescription. Only different points are described.

The welding apparatus according to the second case is a pulse MAGwelding apparatus comprising the following functions: The first arcvoltage value setting circuit VS1 and a second arc voltage value settingcircuit VS2 are to set the arc voltage values at the first weldingcondition and the second welding condition, respectively and output thefirst arc voltage setting signal Vs1 and the second arc voltage settingsignal Vs2, respectively.

An arc voltage switching circuit SW6 outputs an arc voltage switchingsignal S1 by switching between a first arc voltage setting signal Vs1and the second arc voltage setting signal Vs2 with the switching signalH1 The second comparison circuit CM2 outputs the arc voltage controlsignal from the difference between the signal S6 and the arc voltagedetection signal Vd of the arc voltage detection circuit VD.

A pulse frequency signal generator circuit VF3 outputs a signal underswitching, with a switching frequency F of the switching signal H1,between the pulse frequency control signal Vf31 corresponding to firstwelding condition and the second pulse frequency control signal Vf32corresponding to the second welding condition in accordance with the arcvoltage control signal Cm2. A pulse duration frequency signal generatorDF3 outputs the first pulse duration frequency signal Df31 consisting ofthe first pulse frequency signal Vf31 and the first pulse durationsignal Tp1 in accordance with the first welding condition and the pulseduration frequency signal Df32 in accordance with the second weldingcondition in a similar way to that of the first pulse duration frequencysignal Df31. A base pulse current switching circuit SW5 outputs thepulse control signal Pf1 obtained by switching between the pulse currentvalue setting signal Ip1 and the base current setting signal Ib1 withthe first pulse duration frequency signal Df31 at the first weldingcondition and the pulse control signal Pf2 obtained by switching betweenthe pulse current value setting signal Ip1 and the base current settingsignal Ib1 with the second pulse duration frequency signal Df32 at thesecond welding condition. Both pulse control signals Pf1 and Pf2 areinputted to the welding power control circuit PS.

Description of FIG. 97

In FIG. 97, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP1, a firstpulse duration TP1, a first pulse frequency f3 and a first base currentIB1. Reference characters P2, P2, . . . P2 denote a second pulse currentgroup consisting of a second pulse current value IP1 the same as thefirst pulse current value, a second pulse duration TP1 the same as thefirst pulse duration, a second pulse frequency f3 the same as the firstpulse frequency and a second base current IB1 the same as the first basecurrent. Others are the same as those of FIG. 92 and should be omitted.

The welding apparatus according to third case when arc voltage iscontrolled by pulse frequency comprises the following functions: Asecond pulse base current setting circuit for outputting the secondpulse base current setting signal comprises a second arc voltage valuesetting circuit VS2 for setting the arc voltage value setting signalVs2, a second pulse duration setting circuit TP2 for setting a secondpulse duration setting signal Tp2, a second base current setting circuitIB2 for setting a second base current setting signal Ib2 and a secondpulse current value setting circuit IP2 for outputting a second pulsecurrent value setting signal Ip2.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit SW6 for outputting an arcvoltage switching signal S1 by switching between a first arc voltagesetting signal Vs1 corresponding to the first arc length and the secondarc voltage setting signal Vs2 corresponding to the second arc length, apulse current value switching circuit SW1 for outputting a pulse currentswitching signal S1 by switching between a first pulse current settingsignal Ip1 and the second pulse current setting signal Ip2 and a pulseduration switching circuit SW2 for outputting a pulse duration switchingsignal S2 by switching between the first pulse duration setting signalTp1 and the second pulse duration setting signal Tp2 and a base currentswitching circuit SW3 for outputting a base current switching signal S3obtained by switching the first base current setting signal Ib1 and thesecond base current setting signal Ib2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf3 upon receiving the arc voltage controlsignal Cm2, a pulse duration frequency signal generator DF3 foroutputting the first pulse duration frequency signal Df31 consisting ofthe pulse frequency signal Vf3 and the first pulse duration signal Tp1and the pulse duration frequency signal Df32 consisting of the pulsefrequency signal Vf3 and the pulse duration signal Tp2 and a base pulsecurrent switching circuit SW5 for switching between the pulse currentvalue switching signal S1 and the base current switching signal S3 withthe first pulse duration frequency signal Df31 and the second pulseduration frequency control signal Df32.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF3 for outputting the pulsefrequency control signal Vf31 corresponding to the arc voltage settingsignal Vs1 and the second pulse frequency control signal Vf32corresponding to the second arc voltage setting signal Vs1, a pulseduration frequency signal generator DF3 for outputting the first pulseduration frequency signal Df31 consisting of the first pulse frequencysignal Vf31 and the first pulse duration signal Tp1 and the pulseduration frequency signal Df32 consisting of the second pulse frequencysignal Vf32 and the pulse duration signal Tp1 and a base pulse currentswitching circuit SW5 for switching between the pulse current valuesetting signal Ip1 and the base current setting signal Ib1 with thefirst pulse duration frequency signal Df31 and the second pulse durationfrequency control signal Df32.

Description of FIG. 89

FIG. 89 is a block diagram of the embodiment of the welding methodhaving the welding waveform shown in FIG. 96.

In FIG. 89, the structures the same as those of FIG. 87 are denoted withthe characters the same as those of FIG. 87 and are omitted in thedescription. Only different points are described.

In FIG. 89, a first point different from that of FIG. 87 is that thestructure in FIG. 89 comprises a first arc voltage setting circuit VS1and the second arc voltage setting circuit VS2 in place of the arcvoltage setting circuit VS1 of FIG. 87. These circuits set the averagevalues of arc voltage at the first pulse duty time T1 and the secondpulse duty time T2 and output the first arc voltage setting signal Vs1and the second arc voltage setting signal Vs2. An arc voltage switchingcircuit SW6 outputs an arc voltage switching signal S6 by switchingbetween a first arc voltage setting signal Vs1 and the second arcvoltage setting signal Vs2 with the switching signal H1. The secondcomparison circuit CM2 outputs an arc voltage control signal Cm2 fromthe difference between the signal S1 and the arc voltage detectionsignal Vd of the arc voltage detection circuit VD. A pulse frequencysignal generator circuit VF3 outputs the pulse frequency control signalVf3 obtained by switching between the first pulse frequency controlsignal Vf31 corresponding to the first welding condition and the secondpulse frequency control signal Vh32 corresponding to the second weldingcondition with a switching frequency of a switching signal H1 uponreceiving the arc voltage control signal Cm2. A pulse duration frequencysignal generator DF3 outputs the first pulse duration frequency signalDf31 consisting of the pulse frequency signal Vf3 and the first pulseduration signal Tp1 at the first welding condition and the pulseduration frequency signal Df3 consisting of the pulse frequency signalVf3 and the pulse duration signal Tp2 at the second welding condition. Abase pulse current switching circuit SW5 outputs a pulse control signalPf1 obtained by switching between the pulse current value setting signalIp1 of the signa S1 and the base current setting signal Ib1 of thesignal S3 with the first pulse duration frequency signal Df31 and asecond pulse control signal Pf2 obtained by switching between the secondpulse current value setting signal Ip2 of the second signal S2 and thebase current setting signal Ib21 of the signal S3 with the second pulseduration frequency signal Df32. Both signals Pf1 and Pf2 are inputted tothe welding power control circuit PS.

The description with reference to FIGS. 87 and 89 is directed to thewelding apparatus comprising the second pulse current value settingcircuit IP2, the second pulse duration setting circuit TP2 and thesecond base current setting circuit IB2. An apparatus comprising one ortwo of these setting circuits is included within the scope of the firstand third cases when arc voltage is controlled by pulse frequency asshown in the first to fifth embodiments of claim 31. The weldingapparatus shown in FIG. 89 comprises a wire feeding rate switchingcircuit SW7 for a wire feeding rate switching signal S7 by switchingbetween the first welding current setting signal Im1 sent from the firstwelding current setting circuit IM1 and the second welding currentsetting signal Im2 sent from the second welding current setting circuitIM2 as shown in FIG. 89. These structures are not necessary for thethird case described hereinabove.

Description of FIGS. 90 and 91

FIG. 90 is a block diagram of a circuit from the input of the arcvoltage detection signal Vd to the output of the pulse durationfrequency control signal Df3 selected from the block diagram of theembodiment of the welding apparatus of the first and third cases of thepresent invention. FIG. 91 is a graph showing the time passage of theinput signal and the output signal at the various stages of the circuitshown in FIG. 90. The input signal and the output signal of the circuitof FIG. 90 are described as follows: A reference character VE denotes aflat circuit for outputting a flat signal Ve shown in FIG. 91 (A) uponreceiving the arc voltage detection signal Vd. A reference character CM2denotes a second comparison circuit for outputting the arc voltagecontrol signal Cm2 shown in FIG. 91 (C) upon receiving the flat signalVe and an arc voltage setting signal Vs1 shown in FIG. 91 (B) or the arcvoltage switching signal S6. A reference character VFC denotes a Vfconvertor for outputting the pulse frequency signal Vfc shown in FIG. 91(D) having a frequency corresponding to the arc voltage control signalCm2. A reference character TRG denotes a trigger circuit for outputtinga trigger signal Trg in a given pulse duration shown in FIG. 91 (E) in asynchronizing way with the pulse frequency signal Vfc. A referencecharacter TP1 or SW2 is a pulse duration setting circuit TP1 or thepulse duration switching circuit SW2 for outputting the pulse durationsetting signal Tp1 or the pulse duration switching signal S2. Areference character DF3 denotes a pulse duration frequency controlcircuit comprising mono-multi vibrator circuit for outputting the pulseduration frequency control signal Df3 shown in FIG. (F) upon receivingthe trigger signal and the pulse duration setting signal Tp1 or theswitching pulse duration signal S2. It is noted that the circuit or thesignal having the same reference character as each other between FIGS.90 and 83 have the same circuit or the same signal.

Described hereinbelow are three cases of the present invention where thearc voltage is controlled by the pulse duration. As described above, thepulse base current control circuit for outputting the pulse base currentcontrol signal is a comparison circuit CM2 for outputting the arcvoltage control signal Cm2 to control the pulse duration. A first pulsebase current setting circuit for outputting the first pulse base currentsetting signal comprises a pulse frequency setting circuit FP1 forsetting a pulse frequency setting signal Fp1, a base current settingcircuit IB1 for setting a base current setting signal Ib1 and a pulsecurrent value setting circuit IP1 for outputting a pulse current valuesetting signal Ip1.

The welding apparatus according to a first case when arc voltage iscontrolled by pulse duration comprises the following functions: A secondpulse base current setting circuit for outputting the second pulse basecurrent setting signal comprises a second pulse frequency settingcircuit FP2 for setting a second pulse frequency setting signal Fp2, asecond base current setting circuit IB2 for setting a second basecurrent setting signal Ib2 and a second pulse current value settingcircuit IP2 for outputting a second pulse current value setting signalIp2.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current switching circuit Sw1 for outputting a pulsecurrent value switching signal S1 by switching between a pulse currentvalue setting signal Ip1 and the second pulse current setting signalIp2, a base current switching circuit SW3 for outputting a base currentswitching signal S3 obtained by switching the first base current settingsignal Ib1 and the second base current setting signal Ib2 and a pulsefrequency switching circuit SW4 for outputting pulse frequency switchingsignal S4 by switching between the pulse frequency setting signal Fp1and the second frequency setting signal Fp2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the first pulsefrequency signal Vf1 and the second pulse frequency signal Vf2 uponreceiving the pulse frequency switching signal S4, a pulse durationfrequency signal generator DF3 for outputting the first pulse durationfrequency signal Df31 consisting of the pulse frequency signal Vf1 andthe pulse duration signal Tp2 corresponding to the arc voltage controlsignal Cm2 and the pulse duration frequency signal Df32 consisting ofthe second pulse frequency signal Vf2 and the pulse duration signal Tp2and a base pulse current switching circuit SW5 for switching between thepulse current value switching signal S1 and the base current switchingsignal S3 with the first pulse duration frequency signal Df31 and thesecond pulse duration frequency control signal Df32.

Description of FIG. 98

FIG. 98 is a block diagram of the embodiment of the welding methodhaving the welding waveform shown in FIG. 102.

In FIG. 98, the structures the same as those of FIG. 83 are denoted withthe characters the same as those of FIG. 87 and are omitted in thedescription. Only different points are described.

A first pulse current setting circuit IP1 and a second pulse currentvalue setting circuit IP2 outputs a first pulse current setting signalIp1 and a second pulse current value setting signal Ip2.

A pulse current switching circuit Sw1 outputs a pulse current valueswitching signal S1 by switching between a pulse current value settingsignal Ip1 and the second pulse current setting signal Ip2 withswitching signal H1. A first pulse frequency setting circuit FP1 and asecond pulse frequency setting circuit FP2 set first pulse frequency f1and a second pulse frequency f2, respectively and output the first pulsefrequency setting signal Fp1 and the second pulse frequency settingsignal Fp2, respectively. A pulse frequency switching circuit SW4outputs a pulse frequency switching signal S4 obtained by switching thefirst pulse frequency setting signal Fp1 and the second pulse frequencysetting signal Fp2. A pulse frequency signal generator circuit VFoutputs the first pulse frequency signal Vf1 and the second pulsefrequency signal Vf2 upon receiving the pulse frequency switching signalS4. A pulse duration frequency signal generator DF3 outputs the firstpulse duration frequency signal Df31 consisting of the pulse frequencysignal Vf1 and the pulse duration signal Tp2 corresponding to the arcvoltage control signal Cm2 and the pulse duration frequency signal Df32consisting of the second pulse frequency signal Vf2 and the pulseduration signal Tp2. A base pulse current switching circuit SW5 outputsthe first pulse control signal Pf1 obtained by switching between asignal energizing the first pulse current setting signal Ip1 at a periodcorresponding to the pulse duration determined by the pulse durationcontrol signal formed into the first pulse duration frequency controlsignal Df31 and the base current setting signal Ib1 with the first pulseduration frequency signal Df31 and the second pulse control signal Pf2obtained by switching between a signal energizing the second pulsecurrent setting signal Ip2 at a period corresponding to the pulseduration determined by the pulse duration control signal formed into thesecond pulse duration frequency control signal Df32 and the base currentsetting signal Ib2 with the second pulse duration frequency signal Df32.control signal Df32. Both pulse control signals Pf1 and Pf2 are inputtedto the welding power control circuit PS.

Description of FIG. 102

In FIG. 102, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP1, a firstpulse duration TP3, a first pulse frequency f1 and a first base currentIB1. Reference characters P2, P2, . . . P2 denote a second pulse currentgroup consisting of a second pulse current value IP2, a second pulseduration TP3, a second pulse frequency f2 and a second base current IB2.Reference characters M1 and M2 denote the average value of the weldingcurrent at the first pulse current duty time T1 and the second pulseduty time T2. A reference character Ia is an average value of a weldingcurrent.

The description with reference to FIG. 102 is directed to a case whenthe value of the second welding condition is larger than that of thefirst welding condition, that is, IP1<IP2, FP1<FP2,or IB1<IB2. However,the condition Mi<M2 permits the value of the second welding conditionlower than that of the first welding condition; that is IB1>IB2, whenIP1<IP2, and FP1<FP2. Others are the same as the those in FIG. 92 andshould be omitted.

The welding apparatus according a second case when arc voltage iscontrolled by pulse duration comprises the following functions: A secondpulse base current setting circuit for outputting the second pulse basecurrent setting signal comprises a second arc voltage setting circuitVS2 for setting a second arc voltage setting signal Vs2, a base currentsetting circuit IB1 for setting a base current setting signal Ib1 and apulse current value setting circuit IP1 for outputting a pulse currentvalue setting signal Ip1.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit Sw6 for outputting an arcvoltage switching signal S6 by switching between an arc voltage settingsignal Va1 corresponding to the first arc length and the second arcvoltage setting signal Vs2 corresponding to the second arc length.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the first pulsefrequency signal Vf1 upon receiving the pulse frequency setting signalFp1, a pulse duration frequency signal generator DF3 for outputting thefirst pulse duration frequency signal Df31 consisting of the pulsefrequency signal Vf1 and the pulse duration signal Tp31 corresponding tothe arc voltage setting signal Vs1 and the pulse duration frequencysignal Df32 consisting of the pulse frequency signal Vf1 and the pulseduration signal Tp32 corresponding to the second arc voltage settingsignal Vs2 and a base pulse current switching circuit SW5 for switchingbetween the pulse current value setting signal Ip1 and the base currentsetting signal Ib1 with the first pulse duration frequency signal Df31and the second pulse duration frequency control signal Df32.

Description of FIG. 99

FIG. 99 is a block diagram of the embodiment of the welding methodhaving the welding waveform shown in FIG. 103.

In FIG. 99, the structures the same as those of FIG. 98 are denoted withthe characters the same as those of FIG. 87 and are omitted in thedescription. Only different points are described.

A first arc voltage setting circuit VS1 and a second arc voltage settingcircuit VS2 set an average values at a first pulse duty time T1 and asecond pulse duty time T2, respectively and output the first arc voltagesetting signal Vs1 and a second arc voltage setting signal Vs2,respectively. An arc voltage switching circuit Sw6 outputs an arcvoltage switching signal S6 by switching between an arc voltage settingsignal Vs1 and the second arc voltage setting signal Vs2 with answitching signal H1. A second comparison circuit CM2 outputs the arcvoltage control signal Cm2 from the difference between the signal S6 andthe arc voltage detection signal Vd of the arc voltage detection circuitVd. A pulse frequency setting circuit FP1 outputs the pulse frequencysetting signal Fp1 corresponding to the pulse duration (D1=D2).

A pulse frequency signal generator circuit VF outputs the first pulsefrequency signal Vf1 upon receiving the pulse frequency setting signalFp1. A pulse duration frequency signal generator DF3 outputs the firstpulse duration frequency signal Df31 consisting of the pulse frequencysignal Vf1 and the first arc voltage control signal Cm2 controlling thepulse duration corresponding to the first arc voltage setting signal Vs1and the pulse duration frequency signal Df32 consisting of the pulsefrequency signal Vf1 and the second arc voltage control signal Cm2controlling the pulse duration corresponding to the second arc voltagesetting signal Vs2. A base pulse current switching circuit SW5 outputsthe pulse control signal Pf1 obtained by switching, with the first pulseduration frequency control signal Df31, between a signal energizing thepulse current value setting signal Ip1 at the period corresponding tothe pulse duration determined by the pulse duration controlling signalformed into a first pulse duration frequency control signal Df31 and thepulse control signal Pf2 obtained by switching, with the second pulseduration frequency control signal Df32, between a signal energizing thepulse current value setting signal Ip2 at the period corresponding tothe pulse duration determined by the pulse duration controlling signalformed into a second pulse duration frequency control signal Df32. Bothpulse control signals Pf1 and Pf2 are putted into the welding powercontrol circuit PS.

Description of FIG. 103

In FIG. 103, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP1, a firstpulse duration TP31, a first pulse frequency f1 and a first base currentIB1. Reference characters P2, P2, . . . P2 denote a second pulse currentgroup consisting of a second pulse current value IP1 the same as thefirst pulse current value, a second pulse duration TP32, a second pulsefrequency f1 the same as the first pulse frequency and a second basecurrent IB1 the same as the first base current. others are the same asthe those of FIG. 92 and should be omitted.

The welding apparatus according to a third case when arc voltage iscontrolled by pulse duration comprises the following functions: A secondpulse base current setting circuit for outputting the second pulse basecurrent setting signal comprises a second arc voltage setting circuitVS2 for setting a second arc voltage setting signal Vs2, a second pulsecurrent value setting circuit IP2 for outputting a second pulse currentvalue setting signal Ip2 and a second base current setting circuit IB2for setting a base current setting signal Ib2.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit Sw6 for outputting an arcvoltage switching signal S6 by switching between an arc voltage settingsignal Vs1 corresponding to the first arc length and the second arcvoltage setting signal Vs2 corresponding to the second arc length, apulse current value switching circuit SW1 for outputting the pulsecurrent value switching signal S1 obtained by switching between thepulse current value setting signal Ip1 and the second pulse currentvalue setting signal Ip2, a pulse frequency switching circuit SW4 foroutputting the pulse frequency switching signal S4 obtained by switchingthe pulse frequency setting signal Fp1 and the second pulse frequencysetting signal Fp2 and a base current value switching circuit SW3 foroutputting the base current value switching signal S3 obtained byswitching between the base current value setting signal Ib1 and thesecond base current value setting signal Ib2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the first pulsefrequency signal Vf1 and the second pulse frequency signal Vf2 uponreceiving the pulse frequency switching signal S4, a pulse durationfrequency signal generator DF3 for outputting the first pulse durationfrequency signal Df31 consisting of the pulse frequency signal Vf1 andthe pulse duration signal Tp31 corresponding to the arc voltage settingsignal Vs1 and the pulse duration frequency signal Df32 consisting ofthe pulse frequency signal Vf1 and the pulse duration signal Tp32corresponding to the second arc voltage setting signal Vs2 and a basepulse current switching circuit SW5 for switching between the pulsecurrent value switching signal S1 and the base current switching signalS3 with the first pulse duration frequency signal Df31 and the secondpulse duration frequency control signal Df32.

Description of FIG. 100

FIG. 100 is a block diagram of the embodiment of the welding methodhaving the welding waveform shown in FIG. 102.

In FIG. 100, the structures the same as those of FIG. 98 are denotedwith the same characters the same as those of FIG. 98 and are omitted inthe description. Only different points are described.

In FIG. 100, a first point different from that of FIG. 98 is that thestructure in FIG. 100 comprises a first arc voltage setting circuit VS1and the second arc voltage setting circuit VS2 in place of the arcvoltage setting circuit VS1 of FIG. 98. These circuits set the averagevalues of arc voltage at the first pulse duty time T1 and the secondpulse duty time T2 and output the first arc voltage setting signal Vs1and the second arc voltage setting signal Vs2. An arc voltage switchingcircuit SW6 outputs an arc voltage switching signal S6 by switchingbetween a first arc voltage setting signal Vs1 and the second arcvoltage setting signal Vs2 with the switching signal H1. The secondcomparison circuit CM2 outputs an arc voltage control signal Cm2 fromthe difference between the signal S1 and the arc voltage detectionsignal Vd of the arc voltage detection circuit VD. A pulse frequencysignal generator circuit VF outputs the pulse frequency signal Vf1 andthe second pulse frequency signal Vf2 with a switching frequency of aswitching signal H1 upon receiving the pulse frequency switching signalD4. A pulse duration frequency signal generator DF3 for outputting thefirst pulse duration frequency signal Df31 corresponding to the firstpulse duration control signal and the first pulse frequency settingsignal Fp1 and the second pulse duration frequency signal Df32corresponding to the second pulse duration control signal and the secondpulse frequency setting signal Fp2. A base pulse current switchingcircuit SW5 outputs a pulse control signal Pf1 obtained by switchingbetween the pulse current value setting signal Ip1 of the signa S1 andthe base current setting signal Ib1 of the signal S3 with the firstpulse duration frequency signal Df31 and a second pulse control signalPf2 obtained by switching between the second pulse current value settingsignal Ip2 of the second signal S2 and the base current setting signalIb21 of the signal S3 with the second pulse duration frequency signalDf32. Both signals Pf1 and Pf2 are inputted to the welding power controlcircuit PS.

A second different point between the structures of FIGS. 100 and 98 isthat the welding apparatus according to FIG. 100 comprises, in place ofthe average current value setting circuit IM in FIG. 99, the firstwelding current setting circuit IM1 for outputting the first weldingcurrent setting signal Im1, and the second welding current settingcircuit IM2 for outputting the second welding current setting signal Im2and the wire feeding rate switching circuit SW7 for sending the firstcomparison circuit CM1 the wire feeding rate switching signal S7obtained by switching between the first welding current setting signalIm1 and the second welding current setting signal Im2 with a switchingsignal H1.

These additional circuits can achieve the following effects. The averagevalues of welding current M1 and M2 at the first pulse duty time T1 andthe second pulse duty time T2 can be obtained by switching the wirefeeding rate between the first welding current setting circuit Im1 andthe second welding current setting circuit IM2. The above effectachieved by switching the arc length can be enlarged by changingperiodically the average values Mi and M2 within a range to maintain thespray transfer mode at the each of the pulse duty times T1 and T2.Specially, in a case of the enlarged gap of the joint, an increase inthe welding current due to the increase in the wire feeding rate resultsin the increase in the molten metal amount. Thus, the enlarged gap canbe filled with the increased molten metal and causes the resultant beadto form a beautiful appearance. On the other hand, in a case when thejoint gap is smaller, the decrease in the welding current can make themolten metal amount decreased. the smaller gap can be filled with thedecreased molten metal amount and causes the resultant bead to form abeautiful appearance.

The description with reference to FIGS. 98 and 100 is directed to a casewhen the welding apparatus comprises the second pulse current settingcircuit IP2, the second pulse frequency setting circuit FP2 and thesecond base current setting circuit IB2. The welding apparatuscomprising one or two circuits is included in the scope of the first andthird cases when arc voltage is controlled by pulse duration.

Further, the welding apparatus shown in FIG. 100 comprises a wirefeeding rate switching circuit SW7 for outputting the wire feeding rateswitching signal S7 obtained by switching the first welding currentsetting signal Im1 generated from the first welding current settingcircuit IM1 and the second welding current setting signal Im2 generatedfrom the second welding current setting circuit IM2. This structure isnot necessary for the structure of the welding apparatus according tothe third case described hereinabove.

Description of FIG. 101

FIGS. 101 (A) to (E) are graphs showing the waveform of the pulseduration control signals shown in the block diagrams in FIGS. 98 to 100.FIG. 100 (A) shows a case when the arc voltage detection signal Vddecreases gradually in the waveform with time. FIG. 100 (B) shows thetime variation of the first and the second arc voltage setting signalsVs1 and Vs2. FIG. 100(C) shows the time variation of the arc voltagecontrol signal Cm2 which increases gradually with time in accordancewith the arc voltage detection signal Vd shown in FIG. 100 (A). FIG. 100(D) shows the time variation of the pulse frequency signal Vf1. FIG. 100(E) shows the time variation of the pulse duration frequency controlsignal Df3 generated from the pulse duration frequency control signalgenerator DF3. It is seen that the pulse duration frequency signal Df3decreases gradually in the pulse duration (TP1 to TPn) in accordancewith the increase in the arc voltage control signal Cm2.

Described hereinbelow are three cases of the present invention when thestructure according to claim 30 has the arc voltage controlled with thebase current value. A pulse base current control circuit for outputtingthe pulse base current control signal comprises a base current controlcircuit IB3 for outputting the base current control signal Ib3 uponreceiving the arc voltage control signal Cm 2. A first pulse basecurrent setting circuit for outputting the first pulse base currentsetting signal comprises a pulse current value setting circuit IP1 forsetting the pulse current value setting signal Ip1, a pulse durationsetting circuit TP1 for setting a pulse duration setting signal Tp1 anda pulse frequency setting circuit FP1 for setting a pulse frequencysetting signal Fp1.

A welding apparatus according to a first embodiment when arc voltage iscontrolled by base current value comprises the following functions: Asecond pulse base current setting circuit for outputting the secondpulse base current setting signal comprises a second pulse current valuesetting circuit IP2 for setting the second pulse current value settingsignal Ip2, a second pulse duration setting circuit TP2 for setting asecond pulse duration setting signal Tp2 and a second pulse frequencysetting circuit FP2 for setting a second pulse frequency setting signalFp2.

A switching setting circuit for outputting a switching setting signalcomprises a pulse current value switching circuit SW1 for outputting aswitching pulse current value signal S1 obtained by switching betweenthe pulse current value setting signal Ip1 and the second pulse currentsetting signal Ip2, a pulse duration switching circuit SW2 foroutputting a pulse duration switching duration signal S2 obtained byswitching between the pulse duration setting signal Tp1 and the secondpulse duration setting signal Tp2, and a pulse frequency switchingcircuit SW4 for outputting pulse frequency switching signal S4 obtainedby switching between pulse frequency setting signal Fp1 and the secondfrequency setting signal Fp2.

A pulse control signal generator for receiving the pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the first pulsefrequency signal Vf1 and the second frequency signal Vf2 upon receivingthe pulse frequency switching signal S4, a pulse duration frequencysignal generator DF for outputting the first pulse duration frequencysignal Df1 consisting of the first pulse frequency signal Vf1 and thefirst pulse duration signal Tp1 and the second pulse duration frequencysignal Df2 consisting of the second pulse frequency signal Vf2 and thesecond pulse duration signal Tp2, and a base pulse current switchingcircuit SW5 for switching between the pulse current value switchingsignal S1 and the arc voltage switching signal S6 with the first pulseduration frequency signal Df1 and the second pulse duration frequencysignal Df2.

Description of FIG. 104

FIG. 104 is a block diagram of the embodiment for generating the waveform shown in FIG. 107.

In FIG. 104, the constructions the same as those of FIG. 83 have thesame reference characters as those of FIG. 83 and are omitted in thedescription. The different parts only are described.

The welding apparatus according to the first embodiment when arc voltageis controlled by base current value comprises a base current controllingcircuit IB3 and switching signal generator H1 for outputting theswitching signal H1 obtained by switching between the first pulse dutytime T1 and the second duty time T2. At the first pulse duty time T1,the switching signal H1 causes to energize the first pulse current groupdetermined by the pulse current value and pulse duration and the firstbase current value controlled by the pulse period and the first arcvoltage control signal Cm2 at the small arc length. At the second pulseduty time T2, the switching signal H1 causes to energize the secondpulse current group determined by the pulse current value and pulseduration and the second base current value controlled by the pulseperiod and the second arc voltage control signal Cm2 at the long arclength. Further, the various setting values of the first pulse currentgroup and the second pulse current group are set to change the arclength at the first pulse duty time T1 and the arc length at the secondpulse duty time T2 by carrying out the following steps: The first basecurrent value IB31 of the first pulse duty time T1 is set as a value toform a plurality of pulses to one molten metal transfer mode at theshort arc length. On the other hand, the second base current value IB32is changed within the range to form the one pulse to one molten metaltransfer or one pulse to plurality of molten metals transfer mode at thelong arc length.

The first pulse current value setting circuit IP1 and the second pulsecurrent value setting circuit IP2 are to set the first pulse currentvalue IP1 and the second pulse current value IP2, respectively andoutput the first pulse current value setting signal Ip1 and the secondpulse current value setting signal Ip2, respectively. A pulse currentvalue switching circuit SW1 outputs the pulse current value switchingsignal S1 obtained by switching between the signal Ip1 and the signalIP2 with the switching signal H1.

The first pulse duration setting circuit TP1 and the second pulseduration setting circuit TP2 are to set the first pulse duration TP1 andthe second pulse duration TP2, respectively and output the first pulseduration setting signal Tp1 and the second pulse duration setting signalTp2, respectively. A pulse duration switching circuit SW2 outputs thepulse duration switching signal S2 obtained by switching between thesignal Tp1 and the signal TP2 with the switching signal H1.

The first pulse frequency setting circuit FP1 and the second pulsefrequency setting circuit FP2 are to set the first pulse frequency FP1and the second pulse frequency FP2, respectively and output the firstpulse frequency setting signal Fp1 and the second pulse frequencysetting signal Fp2, respectively. A pulse frequency switching circuitSW4 outputs the pulse frequency switching signal S4 obtained byswitching between the signal Fp1 and the signal FP2 with the switchingsignal H1.

A pulse frequency signal generator circuit VF outputs the first pulsefrequency signal Vf1 and the second frequency signal Vf2 upon receivingthe pulse frequency switching signal S4. A pulse duration frequencysignal generator DF outputs the first pulse duration frequency signalDf1 corresponding to the first pulse frequency signal Vf1 and the firstpulse duration signal Tp1 and the second pulse duration frequency signalDf2 corresponding to the second pulse frequency signal Vf2 and thesecond pulse duration signal Tp2. A base pulse current switching circuitSW5 outputs a pulse control signal Pf1 obtained by switching, with thefirst pulse duration frequency signal Df1, between the first basecurrent control signal Ib31 and a signal for energizing the first pulsecurrent value setting signal Ip1 at the period corresponding to thepulse duration determined by the pulse duration setting signal Tp1 whichis formed into the first pulse duration frequency signal Df1 at thefirst pulse time T1. Next, a base pulse current switching circuit SW5outputs a pulse control signal Pf2 obtained by switching, with thesecond pulse duration frequency signal Df2, between the second basecurrent control signal Ib32 and a signal for energizing the second pulsecurrent value setting signal Ip2 at the period corresponding to thepulse duration determined by the second pulse duration setting signalTp2 which is formed into the second pulse duration frequency signal Df2at the second pulse time T2. And both pulse control signals Pf1 and Pf2are outputted to the welding power control circuit PS.

The welding apparatus according to this embodiment comprises at leastone from the group of the second current value setting circuit IP2 andthe second pulse frequency setting circuit FP2 and the second pulseduration setting circuit TP2 in addition to the first pulse currentvalue setting circuit IP1, the first pulse frequency setting circuit FP1and the first pulse duration setting circuit TP1. The switching signalH1 of the switching signal generator HL switches the first pulse dutytime T1 and the second pulse duty time T2 and causes to energize thefirst pulse current group determined by the controlled first basecurrent value IB31, the first pulse current value IP1, the first pulseduration TP1 and the first pulse period D1 at the first pulse duty timeT1. At the second pulse duty time T2, the switching signal H1 causes toenergize the second pulse current group determined by the controlledsecond base current value IB32, the second pulse current value IP2, thesecond pulse duration TP2 and the second pulse period D2.

Description of FIG. 107

In FIG. 107, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP1, a firstpulse duration TP1, a first pulse frequency f1 and a first base currentIB3. Reference characters P2, P2, . . . P2 denote a second pulse currentgroup consisting of a second pulse current value IP2, a second pulseduration TP2, a second pulse frequency f2 and a second base current IB3.

Reference characters M1 and M2 denote the average value of the weldingcurrent at the first pulse current duty time T1 and the second pulseduty time T2, respectively. A reference character Ia is an average valueof a welding current.

The description with reference to FIG. 102 is directed to a case whenthe value of the second welding condition is larger than that of thefirst welding condition, that is, IP1<IP2, FP1<FP2, or TP1<TP2. However,the condition M1<M2 permits the value of the second welding conditionlower than that of the first welding condition; that is FP1>FP2, whenIP1<IP2, and TP1<TP2. Others are the same as the those in FIG. 92 andshould be omitted.

The welding apparatus according to the second embodiment when arcvoltage is controlled by base current value comprises the followingfunctions: A second pulse base current setting circuit for outputtingthe second pulse base current setting signal comprises a second arcvoltage setting circuit VS2 for setting a second arc voltage settingsignal Vs2, a pulse current value setting circuit IP1 for outputting apulse current value setting signal Ip1 and a pulse frequency settingcircuit FP1 for setting a pulse frequency setting signal Ib1.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit SW6 for outputting an arcvoltage switching signal S6 by switching between an arc voltage settingsignal Vs1 corresponding to the first arc length and the second arcvoltage setting signal Vs2 corresponding to the second arc length.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the pulse frequencysignal Vf1 upon receiving the pulse frequency setting signal Fp1, apulse duration frequency signal generator DF for outputting the firstpulse duration frequency signal Df1 consisting of the pulse durationsignal Tp1 and the pulse frequency signal Vf1, and a base pulse currentswitching circuit SW5 for switching between the pulse current valuesignal Ip1 and the base current control signal Ib3 corresponding to thearc voltage switching signal S6 with the first pulse duration frequencysignal Df1.

Description of FIG. 105

FIG. 105 is a block diagram of the embodiment for generating the waveform shown in FIG. 108.

In FIG. 105, the constructions the same as those of FIG. 104 have thesame reference characters as those of FIG. 104 and are omitted in thedescription. The different parts only are described.

In FIG. 105, the first arc voltage setting circuit VS1 and the secondarc voltage setting circuit VS2 are to set the average value of arcvoltage at the first pulse duty time T1 and the second duty time T2,respectively and output the first arc voltage setting signal Vs1 and thesecond arc voltage setting signal Vs2, respectively. An arc voltageswitching circuit SW6 outputs the arc voltage switching signal S6 byswitching between the signals Vs1 and Vs2 with the switching signal H1.The second comparison circuit CM2 outputs the arc voltage control signalCm2 from the difference between the signal S6 and the arc voltagedetection signal Vd of the arc voltage detection circuit VD. The basecurrent control circuit IB3 outputs the first base current controlsignal Ib3 and the second base current control signal Ib32 correspondingto the first base current value IB32 and the second base value IB 32upon receiving the first arc voltage control signal Cm2 at the firstpulse duty time T1 and the second arc voltage control signal Cm2 at thesecond arc duty time T2.

A pulse current value setting circuit IP1 for setting the pulse currentvalue outputs the pulse current setting signal Ip1. A pulse frequencysetting circuit FP1 outputs the pulse frequency setting signal Fp1corresponding to the pulse period (D1=D2). The pulse duration settingcircuit TP1 for setting the pulse duration outputs the pulse durationsetting signal Tp1. The pulse frequency signal generator VF outputs thepulse frequency signal Vf1 upon receiving the pulse frequency settingsignal Fp1. The pulse duration frequency signal generator DF outputs thepulse duration frequency signa Df1 consisting of the pulse durationsetting signal Tp1 and the pulse frequency setting signal Vf1. Next, abase pulse current switching circuit SW5 outputs a pulse control signalPf1 obtained by switching, with the first pulse duration frequencysignal Df1, between the first base current control signal Ib31 and asignal for energizing the first pulse current value setting signal Ip1at the period corresponding to the pulse duration determined by thefirst pulse duration setting signal Tp1 which is formed into the firstpulse duration frequency signal Df1 at the first pulse time T2 and apulse control signal Pf2 obtained by switching, with the second pulseduration frequency signal Df2, between the second base current controlsignal Ib32 and a signal for energizing the second pulse current valuesetting signal Ip2 at the period corresponding to the pulse durationdetermined by the second pulse duration setting signal Tp2 which isformed into the second pulse duration frequency signal Df2 at the secondpulse time T2. Both pulse control signals Pf1 and Pf2 are inputted tothe welding current power control circuit PS.

In such a way, the welding apparatus according to FIG. 105 sends thewire feeding motor WA the average current setting signal Im set by theaverage current setting circuit IM. The pulse current group are set orcontrolled so as to be the average current value Ia corresponding to thewire feeding rate and the arc voltage setting value. The weldingapparatus according to the claim does not carry out the process toswitch the average value of the welding current by switching the wirefeeding rate in a different way from the conventional welding apparatusand is not affected by the response delay to the wire feeding motor WM.The welding apparatus according to the claim comprises the base currentcontrol circuit IB3 and a switching signal generator H1 for outputtingthe switching signal H1 obtained by switching between the first pulseduty time T1 and the second pulse duty time T2. At the first pulse dutytime T1, the switching signal H1 causes to energize the first pulsecurrent group determined by the first base current value which iscontrolled by the first arc voltage control signal Cm2 at thepredetermined pulse current value, pulse duration, pulse period and theshort arc length. At the second pulse duty time T2, the switching signalH1 causes to energize the second pulse current group determined by thesecond base current value which is controlled by the second arc voltagecontrol signal Cm2 at the predetermined pulse current value, pulseduration, pulse period and the long arc length. Further, the varioussetting values at the first pulse current group and the second pulsecurrent group are set to be a value to form the plurality of pulses toone molten metal transfer mode or one pulse to one molten metal transfermode of a short arc length at the first pulse duty time T1. At thesecond pulse duty time T2, these values are changed within the range toform the one pulse to one molten metal transfer mode or the one pulse toplurality of molten metal transfer mode at a long arc length. In such away, the welding apparatus according to the claim is in a structure forchanging the arc length at the first pulse duty time T1 and the arclength at the second pulse duty time T2.

Description of FIG. 108

In FIG. 108, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP1, a firstpulse duration TP1, a first pulse frequency f1 and a first base currentIB3. Reference characters P2, P2, . . . P2 denote a second pulse currentgroup consisting of a second pulse current value IP12 the same as thefirst pulse current, a second pulse duration TP1 the same as the firstpulse duration, a second pulse frequency f1 the same as the first pulsefrequency and a second base current IB3.

Reference characters M1 and M2 denote the average value of the weldingcurrent at the first pulse current duty time T1 and the second pulseduty time T2, respectively. A reference character Ia is an average valueof a welding current.

The welding apparatus according to the third embodiment when arc voltageis controlled by base current value comprises the following functions: Asecond pulse base current setting circuit for outputting the secondpulse base current setting signal comprises a second arc voltage settingcircuit VS2 for setting a second arc voltage setting signal Vs2, asecond pulse current value setting circuit IP2 for outputting a secondpulse current value setting signal Ip2, the second pulse durationsetting circuit TP2 for setting the second pulse duration setting signalTp2 and a second pulse frequency setting circuit FP2 for setting asecond pulse frequency setting signal Fp2.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit Sw6 for outputting an arcvoltage switching signal S6 by switching between an arc voltage settingsignal Vs1 corresponding to the first arc length and the second arcvoltage setting signal Vs2 corresponding to the second arc length, apulse current value switching circuit SW1 outputting the pulse currentvalue switching signal S1 obtained by switching between the pulsecurrent value setting signal Ip1 and the second pulse current valuesetting signal Ip2, a pulse duration switching circuit SW2 outputtingthe pulse duration switching signal S2 obtained by switching between thepulse duration setting signal Tp1 and the second pulse duration settingsignal Tp2, and a pulse frequency switching circuit SW4 outputting thepulse frequency switching signal S4 obtained by switching between thepulse frequency setting signal Fp1 and the second pulse frequencysetting signal Fp2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the pulse frequencysignal Vf1 and the second pulse frequency signal Vf2 upon receiving thepulse frequency switching signal S4, a pulse duration frequency signalgenerator DF for outputting the first pulse duration frequency signalDf1 consisting of the pulse frequency signal Vf1 and the pulse durationsignal Tp1, and the second pulse duration frequency signal Df1consisting of the second frequency signal Vf2 and the second pulseduration signal Tp2, and a base pulse current switching circuit SW5 forswitching between the pulse current value switching signal S1 and thebase current control signal Ib3 corresponding to the arc voltageswitching signal S6 with the first pulse duration frequency signal Df1and the second pulse duration frequency signal Df2.

Description of FIG. 106

FIG. 106 is a block diagram of the embodiment for generating the waveform shown in FIG. 107.

In FIG. 106, the constructions the same as those of FIG. 104 have thesame reference characters as those of FIG. 104 and are omitted in thedescription. The different parts only are described.

In FIG. 106, a first different structure form that of FIG. 104 is thatthe first arc voltage setting circuit VS1 and the second arc voltagesetting circuit VS2 are to set the average value of arc voltage at thefirst pulse duty time T1 and the second duty time T2, respectively andoutput the first arc voltage setting signal Vs1 and the second arcvoltage setting signal Vs2 in place of the first arc voltage settingcircuit VS1 shown in FIG. 104. An arc voltage switching circuit SW6outputs the arc voltage switching signal S6 by switching between thesignals Vs1 and Vs2 with the switching signal H1. The second comparisoncircuit CM2 outputs the arc voltage control signal Cm2 from thedifference between the signal S6 and the arc voltage detection signal Vdof the arc voltage detection circuit VD. The base current controlcircuit IB3 outputs the first base current control signal Ib31 and thesecond base current control signal Ib32 corresponding to the first basecurrent value IB32 and the second base value IB 32 upon receiving thefirst arc voltage control signal Cm2 at the first pulse duty time T1 andthe second arc voltage control signal Cm2 at the second arc duty timeT2.

A second different point between the structures in FIGS. 106 and 104 isthat the structure in FIG. 106 comprises the following circuits in placeof the average current value setting circuit IM. The welding apparatusshown in FIG. 106 comprises the first welding current setting circuitIM1 for outputting the first welding current setting signal Im1 and thesecond welding current setting circuit IM2 for outputting the secondwelding current setting signal Im2 and the wire feeding rate switchingcircuit SW7 for sending the first comparison circuit CM1 the wirefeeding rate switching signal S7 obtained by switching between the firstwelding current setting signal Im1 and the second welding currentsetting signal Im2 with the switching signal H1.

Other structures except for the above structures are the same as thoseof FIG. 105 and should be omitted in the description.

The description with reference to FIGS. 104 and 106 is directed to thewelding apparatus comprising the second pulse current setting circuitIP2 and the second pulse duration setting circuit TP2 and the secondpulse frequency setting circuit FP2. The welding apparatus comprisingone or two circuits are included in the scope of the first and thirdcases when arc voltage is controlled by base current value.

Further, the welding apparatus shown in FIG. 106 comprises the wirefeeding rate switching circuit SW7 for outputting the wire feeding rateswitching signal S7 obtained by switching between the first weldingcurrent setting signal Im1 generated from the first welding currentsetting circuit Im1 and the second welding current setting signal Im2generated from the second welding current setting circuit Im2. The abovestructure is not necessary for the structure of the third case describedhereinabove.

Described hereinbelow are three more embodiments of the presentinvention when the structure has the arc voltage controlled with thebase current value. A pulse base current control circuit for outputtingthe pulse base current control signal comprises a pulse current controlcircuit IP3 for outputting the pulse current control signal Ip3 uponreceiving arc voltage control signal Cm 2.

A first pulse base current setting circuit for outputting the firstpulse base current setting signal comprises a pulse duration settingcircuit TP1 for setting the pulse duration setting signal Tp1, a pulsefrequency setting circuit FP1 for setting a pulse frequency settingsignal Fp1 and a base current setting circuit IB1 for setting a basecurrent setting signal Ib1.

The welding apparatus according to a first embodiment when arc voltageis controlled by pulse current value comprises the following functions:A second pulse base current setting circuit for outputting the secondpulse base current setting signal comprises the second pulse durationsetting circuit TP2 for setting the second pulse duration setting signalTp2 and a second pulse frequency setting circuit FP2 for setting asecond pulse frequency setting signal Fp2 and a second base currentvalue setting circuit IB2 for outputting a second base current valuesetting signal Ib2.

A switching setting circuit for outputting a switching setting signalcomprises a pulse duration switching circuit SW2 for outputting a pulseduration switching signal S2 by switching between a pulse durationsetting signal Tp1 and the second pulse duration setting signal Tp2, apulse frequency switching circuit SW4 outputting the pulse frequencyswitching signal S4 obtained by switching between the pulse frequencysetting signal Fp1 and the second pulse frequency setting signal Fp2 anda base current value switching circuit SW3 outputting the base currentvalue switching signal S3 obtained by switching between the base currentvalue setting signal Ib1 and the second base current value settingsignal Ib2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the pulse frequencysignal Vf1 and the second pulse frequency signal Vf2 upon receiving thepulse frequency switching signal S4, a pulse duration frequency signalgenerator DF for outputting the first pulse duration frequency signalDf1 consisting of the pulse frequency signal Vf1 and the pulse durationsignal Tp1, and the second pulse duration frequency signal Df2consisting of the second frequency signal Vf2 and the second pulseduration signal Tp2, and a base pulse current switching circuit SW5 forswitching between the base current value switching signal S3 and thepulse current control signal Ip3 corresponding to the arc voltageswitching signal S6 with the first pulse duration frequency signal Df1and the second pulse duration frequency signal Df2.

Description of FIG. 109

FIG. 109 is a block diagram of the embodiment for generating the waveform shown in FIG. 112.

In FIG. 109, the constructions the same as those of FIG. 83 have thesame reference characters as those of FIG. 83 and are omitted in thedescription. The different parts only are described.

The first pulse duration setting circuit TP1 and the second pulseduration setting circuit TP2 for setting the first pulse durationsetting signal Tp1 and the second pulse duration setting signal Tp2,respectively output the first pulse duration setting signal Tp1 and thesecond pulse duration setting signal Tp2, respectively. A pulse durationswitching circuit SW2 outputs a pulse duration switching signal S2 byswitching between a pulse duration setting signal Tp1 and the secondpulse duration setting signal Tp2 with a switching signal H1.

A first pulse frequency setting circuit FP1 and a second pulse frequencysetting circuit FP2 set a first pulse frequency setting signal Fp1 and asecond pulse frequency setting signal Fp2, respectively. A pulsefrequency switching circuit SW4 outputs the pulse frequency switchingsignal S4 obtained by switching between the pulse frequency settingsignal Fp1 and the second pulse frequency setting signal Fp2.

A first base current value setting circuit IB1 and a second base currentvalue setting circuit IB2 for setting a first base current value settingsignal Ib1 and a second base current value setting signal Ib2 output afirst base current value setting signal Ib1 and a second base currentvalue setting signal Ib2, respectively. A base current value switchingcircuit SW3 outputs the base current value switching signal S3 obtainedby switching between the base current value setting signal Ib1 and thesecond base current value setting signal Ib2.

A pulse frequency signal generator circuit VF outputs the pulsefrequency signal Vf1 and the second pulse frequency signal Vf2 uponreceiving the pulse frequency switching signal S4. A pulse durationfrequency signal generator DF outputs the first pulse duration frequencysignal Df1 consisting of the pulse frequency signal Vf1 and the pulseduration signal Tp1, and the second pulse duration frequency signal Df1consisting of the second frequency signal Vf2 and the second pulseduration signal Tp2. A base pulse current switching circuit SW5 outputsa pulse control signal Pf1 obtained by switching, with the first pulseduration frequency signal Df1, between a signal for energizing the firstpulse current control signal Ip31 and the first base current valuesetting signal Ib1 at the period corresponding to the pulse durationdetermined by the first pulse duration setting signal Tp1 which isformed into the first pulse duration frequency signal Df1 at the secondpulse time T1. Next, a base pulse current switching circuit SW5 outputsa pulse control signal Pf2 obtained by switching, with the second pulseduration frequency signal Df2, between a signal for energizing thesecond pulse current control signal Ip32 and the second base currentvalue setting signal Ib2 at the period corresponding to the pulseduration determined by the second pulse duration setting signal Tp2which is formed into the second pulse duration frequency signal Df2 atthe second pulse time T2. And both pulse control signals Pf1 and Pf2 areoutputted to the welding power control circuit.

The welding apparatus according to the fourth embodiment comprises atleast one of the second pulse duration setting circuit TP2 and thesecond pulse frequency setting circuit Fp2 and the second base currentsetting circuit IB2 in addition to the first pulse duration settingcircuit TP1, the first pulse frequency setting circuit Fp1 and the firstbase current setting circuit IB1. The switching signal generator HLoutputs a switching signal H1 by switching between the first pulse dutytime T1 and the second pulse duty time T2. The switching signal causesto energize the first pulse current group determined by the first pulsecurrent value IP31, the first pulse duration Tp1 and the first basecurrent value IB1 at the first pulse duty time T1. On the other hand,the switching signal H1 causes to energize the second pulse currentgroup determined by the second pulse current value IP32, the secondpulse duration Tp2 the second frequency f2 and the second base currentvalue IB2 at the second pulse duty time T2. The various setting valuesat the first pulse current P1 and the second pulse current P2 are set toa specified value. The first pulse current P1 at the first pulseduration time T1 is set to a value to form the plurality of pulse to onemolten metal transfer mode or the one pulse to one molten metaltransfer. The second pulse current P2 at the second pulse duty time T2changes one or more than two of the first pulse duration, the pulsefrequency and the base current value other than the first pulse currentto change within the range to form the one pulse to one molten metaltransfer mode or the one pulse to plurality of molten metal transfermode. Accordingly, the apparatus according to the present invention canchange the arc length at the first pulse duty time T1 and the arc lengthat the second pulse duty time T2.

In such a way, the welding apparatus sends the wire feeding motor WA theaverage current setting signal Im set by the average current settingcircuit IM. The pulse current group are set and controlled so as to bethe average current value Ia corresponding to the wire feeding rate andthe arc voltage setting value. The welding apparatus according to thisembodiment does not carry out the process to switch the average value ofthe welding current by switching the wire feeding rate in a differentway from the conventional welding apparatus and is not affected by theresponse delay to the wire feeding motor WM. The welding apparatusaccording to this embodiment comprises the base current control circuitIB3 and a switching signal generator H1 for outputting the switchingsignal H1 obtained by switching between the first pulse duty time T1 andthe second pulse duty time T2. At the first pulse duty time T1, theswitching signal H1 causes to energize the first pulse current groupdetermined by the first base current value which is controlled by thefirst arc voltage control signal Cm2 at the predetermined pulse currentvalue, pulse duration, pulse period and the short arc length. At thesecond pulse duty time T2, the switching signal H1 causes to energizethe second pulse current group determined by the second base currentvalue which is controlled by the second arc voltage control signal Cm2at the predetermined pulse current value, pulse duration, pulse periodand the long arc length. Further, the various setting values at thefirst pulse current group and the second pulse current group are set tobe a value to form the plurality of pulses to one molten metal transfermode or one pulse to one molten metal transfer mode of a short arclength at the first pulse duty time T1. At the second pulse duty timeT2, these values are changed within the range to form the one pulse toone molten metal transfer mode or the one pulse to plurality of moltenmetal transfer mode at a long arc length. In such a way, the weldingapparatus according this embodiment claim is of a structure capable ofchanging the arc length at the first pulse duty time T1 and the arclength at the second pulse duty time T2.

Description of FIG. 112

In FIG. 112, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP3, a firstpulse duration TP1, a first pulse frequency f1 and a first base currentIB1. Reference characters P2, P2, . . . P2 denote a second pulse currentgroup consisting of a second pulse current value IP3, a second pulseduration TP2, a second pulse frequency f2 and a second base current IB2.

Reference characters M1 and M2 denote the average value of the weldingcurrent at the first pulse current duty time T1 and the second pulseduty time T2, respectively. A reference character Ia is an average valueof a welding current.

The description with reference to FIG. 112 is directed to a case whenthe value of the second welding condition is larger than that of thefirst welding condition, that is, TP1<TP2, FP1<FP2, or IB1<IB2. However,the condition M1<M2 permits the value of the second welding conditionlower than that of the first welding condition; that is IB1>IB2, whenTP1<TP2, and FP1<FP2. Others are the same as the those in FIG. 92 andshould be omitted.

The welding apparatus according to a second embodiment when arc voltageis controlled by pulse current value comprises the following functions:A second pulse base current setting circuit for outputting the secondpulse base current setting signal comprises a second arc voltage settingcircuit VS2 for setting a second arc voltage setting signal Vs2, thesecond pulse duration setting circuit TP2 for setting the second pulseduration setting signal Tp2 and a first pulse frequency setting circuitFP1 for setting a first pulse frequency setting signal Fp1 and a firstbase current value setting circuit IB1 for outputting a first basecurrent value setting signal Ib2.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit SW6 for outputting an arcvoltage switching signal S6 by switching between an arc voltage settingsignal Vs1 corresponding to the first arc length and the second arcvoltage setting signal Vs2 corresponding to the second arc length.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the pulse frequencysignal Vf1 upon receiving the pulse frequency setting signal Fp1, apulse duration frequency signal generator DF for outputting the firstpulse duration frequency signal Df1 consisting of the pulse frequencysignal Vf1 and the pulse duration signal Tp1, and a base pulse currentswitching circuit SW5 for switching between the pulse current valueswitching signal S1 and the base current control signal Ib3corresponding to the arc voltage switching signal S6 with the firstpulse duration frequency signal Df1 and the second pulse durationfrequency signal Df2.

Description of FIG. 110

FIG. 110 is a block diagram of the embodiment for generating the waveform shown in FIG. 113.

In FIG. 110, the constructions the same as those of FIG. 109 have thesame reference characters as those of FIG. 109 and are omitted in thedescription. The different parts only are described.

In FIG. 110, the first arc voltage setting circuit VS1 and the secondarc voltage setting circuit VS2 are to set the average value of arcvoltage at the first pulse duty time T1 and the second duty time T2,respectively and output the first arc voltage setting signal Vs1 and thesecond arc voltage setting signal Vs2, respectively. An arc voltageswitching circuit SW6 outputs the arc voltage switching signal S6 byswitching between the signals Vs1 and Vs2 with the switching signal H1.The second comparison circuit CM2 outputs the arc voltage control signalCm2 from the difference between the signal S1 and the arc voltagedetection signal Vd of the arc voltage detection circuit VD. The pulsecurrent control circuit IP3 outputs the first pulse current controlsignal Ip31 and the second base current control signal Ip32corresponding to the first pulse current value IP31 and the second pulsevalue IP32 upon receiving the first arc voltage control signal Cm2 atthe first pulse duty time T1 and the second arc voltage control signalCm2 at the second arc duty time T2.

A pulse frequency setting circuit FP1 outputs the pulse frequencysetting signal Fp1 corresponding to the pulse period (D1=D2). The pulseduration setting circuit TP1 for setting the pulse duration outputs thepulse duration setting signal Tp1. The base current setting circuit IB1for setting the base current value outputs the base current settingsignal Ib1. The pulse frequency signal generator VF outputs the pulsefrequency signal Vf1 upon receiving the pulse frequency setting signalFp1. The pulse duration frequency signal generator DF outputs the pulseduration frequency signal Df1 consisting of the pulse duration settingsignal Tp1 and the pulse frequency setting signal Vf1. Next, a basepulse current switching circuit SW5 outputs a pulse control signal Pf1obtained by switching, with the first pulse duration frequency signalDf1, between a signal for energizing the pulse current value controlsignal Ip3 and the first base current setting signal Ib31 at the periodcorresponding to the pulse duration determined by the first pulseduration setting signal which is formed into the first pulse durationfrequency signal Df1 at the first pulse time T1 and a pulse controlsignal Pf2 obtained by switching, with the second pulse durationfrequency signal Df2, between a signal for energizing the second pulsecurrent value control signal Ip3 and the second base current settingsignal Ib12 at the period corresponding to the pulse duration determinedby the second pulse duration setting signal Tp2 which is formed into thesecond pulse duration frequency signal Df1 at the second pulse time T2.Both pulse control signals Pf1 and Pf2 are inputted to the weldingcurrent power control circuit PS.

Others are the same as those of FIG. 109 and should be omitted.

Description of FIG. 113

In FIG. 113, reference characters P1, P1, . . . P1 denote a first pulsecurrent group consisting of a first pulse current value IP3, a firstpulse duration TP1, a first pulse frequency f1 and a first base currentIB1. Reference characters P2, P2, . . . P2 denote a second pulse currentgroup consisting of a second pulse current value IP32, a second pulseduration TP1 the same as the first pulse duration, a second pulsefrequency f1 the same as the first pulse frequency and a second basecurrent IB1 the same as the first base current.

Reference characters M1 and M2 denote the average value of the weldingcurrent at the first pulse current duty time T1 and the second pulseduty time T2, respectively. A reference character Ia is an average valueof a welding current.

The welding apparatus according to a third embodiment when arc voltageis controlled by pulse current value comprises the following functions.A second pulse base current setting circuit for outputting the secondpulse base current setting signal comprises the second arc voltagesetting circuit VS2 for outputting the second arc voltage setting signalVs2, the second pulse duration setting circuit TP2 for setting thesecond pulse duration setting signal Tp2 and a second pulse frequencysetting circuit FP2 for setting a second pulse frequency setting signalFp2 and a second base current value setting circuit IB2 for outputting asecond base current value setting signal Ib2.

A switching setting circuit for outputting a switching setting signalcomprises an arc voltage switching circuit SW6 for outputting the arcvoltage switching signal S6 by switching between the arc voltage settingsignal Vs1 corresponding to the first arc length and the second arcvoltage setting signal Vs2 corresponding to the second arc length, apulse duration switching circuit Sw2 for outputting a pulse durationswitching signal S2 by switching between a pulse duration setting signalTp1 and the second pulse duration setting signal Tp2, and a pulsefrequency switching circuit SW4 outputting the pulse frequency switchingsignal S4 obtained by switching between the pulse frequency settingsignal Fp1 and the second pulse frequency setting signal Fp2 and a basecurrent value switching circuit SW3 outputting the base current valueswitching signal S3 obtained by switching between the base current valuesetting signal Ib1 and the second base current value setting signal Ib2.

A pulse control signal generator for receiving pulse base currentcontrol signal and the switching setting signal comprises a pulsefrequency signal generator circuit VF for outputting the pulse frequencysignal Vf1 and the second pulse frequency signal Vf2 upon receiving thepulse frequency switching signal S4, a pulse duration frequency signalgenerator DF for outputting the first pulse duration frequency signalDf1 consisting of the pulse frequency signal Vf1 and the pulse durationsignal Tp1, and the second pulse duration frequency signal Df2consisting of the second frequency signal Vf2 and the second pulseduration signal Tp2, and a base pulse current switching circuit SW5 forswitching between the base current value switching signal S3 and thepulse current control signal Ip3 corresponding to the arc voltageswitching signal S6 with the first pulse duration frequency signal Df1and the second pulse duration frequency signal Df2.

Description of FIG. 111

FIG. 111 is a block diagram of the embodiment for generating the waveform shown in FIG. 112.

In FIG. 111, the constructions the same as those of FIG. 109 have thesame reference characters as those of FIG. 109 and are omitted in thedescription. The different parts only are described.

In FIG. 111, a first different structure from that of FIG. 109 is thatin place of the arc voltage setting circuit VS1 shown in FIG. 109, thefirst arc voltage setting circuit VS1 and the second arc voltage settingcircuit VS2 are to set the average value of arc voltage at the firstpulse duty time T1 and the second duty time T2, respectively and outputthe first arc voltage setting signal Vs1 and the second arc voltagesetting signal Vs2, respectively. An arc voltage switching circuit SW6outputs the arc voltage switching signal S6 by switching between thesignals Vs1 and Vs2 with the switching signal H1. The second comparisoncircuit CM2 outputs the arc voltage control signal Cm2 from thedifference between the signal S6 and the arc voltage detection signal Vdof the arc voltage detection circuit VD. The pulse current controlcircuit IP3 outputs the first pulse current control signal Ip31 and thesecond base current control signal Ip32 corresponding to the first pulsecurrent value IP31 and the second pulse value IP32 upon receiving thefirst arc voltage control signal Cm2 at the first pulse duty time T1 andthe second arc voltage control signal Cm2 at the second arc duty timeT2.

A second different point between the structures in FIGS. 111 and 109 isthat the structure in FIG. 1116 comprises the following circuits inplace of the average current value setting circuit IM. The weldingapparatus shown in FIG. 111 comprises the first welding current settingcircuit IM1 for outputting the first welding current setting signal Im1and the second welding current setting circuit IM2 for outputting thesecond welding current setting signal Im2 and the wire feeding rateswitching circuit SW7 for sending the first comparison circuit CM1 thewire feeding rate switching signal S7 obtained by switching between thefirst welding current setting signal Im1 and the second welding currentsetting signal Im2 with the switching signal H1.

Other structures except for the above structures are the same as thoseof FIG. 109 and should be omitted in the description.

The description with reference to FIGS. 109 and 111 is directed to thewelding apparatus comprising the second pulse duration setting circuitTP2, the second pulse frequency setting circuit FP2 and the second basecurrent setting circuit IB2. The welding apparatus comprising one or twocircuits are included in the scope of the first and third embodimentswhen arc voltage is controlled by pulse current value.

Further, the welding apparatus shown in FIG. 111 comprises the wirefeeding rate switching circuit SW7 for outputting the wire feeding rateswitching signal S7 obtained by switching between the first weldingcurrent setting signal Im1 generated from the first welding currentsetting circuit Im1 and the second welding current setting signal Im2generated from the second welding current setting circuit Im2. The abovestructure is not a necessary factor for the structure of the thirdembodiment described hereinabove.

The welding apparatus according to a final embodiment is based on apulse MAG welding apparatus and comprises the first welding currentsetting circuit IM1 for outputting the first welding current settingsignal Im1, the second welding current setting circuit for outputtingthe second welding current setting signal Im2 and the wire feeding rateswitching circuit SW7 for sending the wire feeding rate control circuitWC the wire feeding rate switching signal S7 obtained by switchingbetween the first welding current setting signal Im1 and the secondwelding current setting signal Im2 with a switching frequency F of 0.5to 5 Hz.

This embodiment, as is shown in FIGS. 89, 100, 106 and 111, andincluding these additional circuits can achieve the following effects.The average values of welding current M1 and M2 at the first pulse dutytime T1 and the second pulse duty time T2 can obtained by switching thewire feeding rate between the first welding current setting circuit IM1and the second welding current setting circuit IM2. The above effectachieved by switching the arc length can be enlarged by switchingperiodically between the first pulse duty time T1 of the short arclength for setting the average values M1 and M2 within a range tomaintain a plurality of pulses to one molten metal transfer mode or theone pulse to one molten metal transfer mode at the first pulse duty ofthe short arc length, and the second pulse duty time T2 of the long arclength for setting the average values M1 and M2 within a range to formthe one pulse to one molten metal transfer mode or one pulse toplurality of molten metal transfer mode. Specially, in a case of theenlarged gap of the joint, an increase in the welding current due to theincrease in the wire feeding rate results in the increase in the moltenmetal amount. Thus, the enlarged gap can be filled with the increasedmolten metal and causes the resultant bead to form a beautifulappearance. On the other hand, in a case when the joint gap is smaller,the decrease in the welding current can make the molten metal amountdecreased. The smaller gap can be filled with the decreased molten metalamount and causes the resultant bead to form a beautiful appearance.

EFFECT OF THE PRESENT INVENTION

The following description is to summarize the effects of the weldingmethod according to the present invention.

(1) The welding for aluminum can achieve the appearance of the bead in aregular ripple pattern. (2) The welding for copper and copper alloy canachieves an appearance of the bead in regular ripple pattern. (3) Thewelding for aluminum can prevent the cracking by making the grain sizesmaller. (4) The welding for aluminum can prevent the generation of theporosity. (5) The butt welding can prevent the melt down even with theenlarged gap of the butt joint. (6) The lap welding can prevent thepartial melting even with the enlarged gap of the lap joint. (7) Thewelding for stainless steel can control the penetration shape and canmake the penetration depth at a constant value in a proceeding directionof the welding bead.

The more detailed description is shown in the following. Theconventional welding method has the disadvantage to make the arc lengthtoo much long and unstable due to the delay of the mechanical variation,to generate more frequently the sputter due to the short circuit and togenerate sometimes the wire extending or the burn back. The weldingmethod according to the present invention can solve these disadvantages.In addition, since the welding method according to the present inventionis not based on a type to obtain the scale bead by switchingperiodically between the spray transfer mode and the short circuittransfer mode, the welding method of the present invention can obtainthe scale bead in a regular ripple pattern in a similar way to that ofthe TIG welding method and also can prevent the generation of thesputter.

Further, the welding method or the apparatus is based on a type tomanage the first pulse current group to be in a plurality of pulses toone molten metal mode or the one pulse to one molten metal transfer modeand makes it possible to decrease the arc length to a minimum value of 2to 3 mm near to the short circuit distance which causes the slight shortcircuits. Therefore, it is possible for the welding method according tothe present invention to carry out the high speed welding for the thinplate in a similar way to that of the pulse arc welding method orapparatus in a conventional mode of one pulse to one molten metaltransfer mode. It is possible to change periodically the arc length byincreasing periodically the arc length with the enlarged value of one ortwo factors of the pulse current, pulse duration, pulse frequency or thebase current value controlled within a range to form the one pulse toone molten metal transfer mode or the one pulse to plurality of moltenmetal transfer mode in connection with the second pulse current group.Hence, the welding method according to the present invention can achievethe various effects to prevent the melt down at the upper plate with thegap at the lap welding or the gap caused by the thermal deformation, toprevent the drop down at the vertical up welding to improve theappearance of the bead and to hold the penetration shape at each ofoscillating positions with the oscillating welding.

As mentioned above, it is possible for the welding method managing thefirst current group to be in a one pulse to one molten metal transfermode or the plurality of pulses to one metal transfer mode according tothe present invention to make the arc length short to a distance of 2 to3 mm to cause the slight short circuits. In addition, the generation ofthe conventional short circuit and the sputter is very few. Inconnection with the second pulse current group, it is possible to makethe arc length of the first pulse current group short by forming the onepulse to one molten metal transfer mode or the one pulse to a pluralityof molten metal transfer mode. Accordingly, the arc length of the secondpulse current group can be made to a short distance of 4 to 5 mm. Theconventional welding method has the disadvantage to make the arc lengthtoo much longer and the arc extended widely at a high current period.The welding method according to present invention can be free from thedisadvantage and thus free from the defect for the gas shield. Thewelding method according to the present invention shows the superiorcharacter with the cleaning process of aluminum welding and is able toprevent the unstable arc in a too much long extension between theconsumable electrode and the cathode of aluminum welding material.

In connection with the MIG arc welding for stainless steel having a lowthermal conductivity, the periodical variation in the arc length makesit possible to control the penetration shape by melting the molten poolsin different penetration shapes into one body. This process can expandthe allowable gap size at the lap welding and the butt welding and holdthe penetration depth at a constant value in a welding direction tocontrol the sectional form of the welding bead.

Further, among the various MAG arc welding method of the presentinvention, in connection with the MIG arc welding for aluminum or copperhaving a high thermal conductivity, the variation in the welding currentdue to the periodical switching of the wire feeding rate can changeperiodically the molten metal amount. This process makes it possible toform the round scale bead in accordance with the variation in the heightof reinforcement. In connection with the MAG arc welding for stainlesssteel having a low thermal conductivity, the periodic variation in thewelding current due to the periodic switching of the wire feeding ratemakes it possible to change the wire melting amount so as to control themolten metal amount of the reinforcement in addition to the effect of aperiodic switching of the arc length.

We claim:
 1. A pulse MAG arc welding apparatus for carrying out an arcwelding operation by supplying a pulse welding current that switchesbetween a first pulse current group for generating a short arc lengthand a second pulse current group for generating a long arc length, saidapparatus comprising:an arc voltage detecting circuit for detecting anarc voltage value and outputting an arc voltage detecting signalcorresponding thereto; a first arc voltage setting circuit for setting avalue of arc voltage in accordance with welding conditions andoutputting a first arc voltage setting signal corresponding thereto; asecond arc voltage setting circuit for setting a value of arc voltage inaccordance with welding conditions and outputting a second arc voltagesetting signal corresponding thereto; a comparison circuit for comparingsaid arc voltage detecting signal with and arc voltage setting signaland outputting a difference between said two signals as an arc voltagecontrol signal; a pulse condition control signal generation circuit forgenerating a pulse condition control signal for controlling onepreselected pulse control condition from among four pulse controlconditions in common with said first and second pulse current groups inaccordance with said arc voltage control signal, said four pulse controlconditions comprising pulse frequency, pulse width, base current valueand peak current value; a pulse current setting circuit for setting theremaining three pulse control conditions for said first pulse currentgroup and said second pulse current group which have not beenpreselected and for outputting pulse current group setting signalsincluding setting signals corresponding to remaining three pulse controlconditions other than said pulse condition control signal; a switchingcircuit for generating a switching signal for switching said first andsecond pulse current setting circuits alternatively at a frequencyranging from 0.5 to 25 Hz; a pulse frequency signal generation circuitfor generating a pulse frequency signal in response to either the pulsefrequency control reference signal if output from said pulse conditioncontrol signal generation circuit, or, the pulse frequency settingsignal output from said pulse current setting circuit if not output fromsaid pulse condition control signal generation circuit; a pulsefrequency and width signal generation circuit for outputting a pulsefrequency and width signal in response to the pulse frequency controlsignal and pulse width setting signal if the pulse frequency controlreference signal is output from said pulse condition control signalgeneration circuit, the pulse frequency signal and pulse width controlsignal if the pulse width control signal is output from said pulsecondition control signal generation circuit, or the pulse frequencysignal and pulse width setting signal if the peak current control signalor base current control signal is output from said pulse conditioncontrol signal generation circuit; a pulse current control circuit foroutputting a first pulse control signal and a second pulse controlsignal alteratively in response to the pulse frequency and width signal,the peak current setting signal and base current setting signal if thepulse frequency control reference signal or the pulse width controlsignal is output from said pulse condition control signal generationcircuit, the pulse frequency and width signal, the peak current controlsignal and base current setting signal if the peak current controlsignal is output from said pulse condition control signal generationcircuit, or the pulse frequency and width signal, the peak currentsetting signal and base current control signal if the base currentcontrol signal is output from said pulse condition control signalgeneration circuit; and a welding power source control circuit foroutputting the first pulse current group when the first pulse controlsignal is output from said pulse current control circuit and the secondpulse current group when the second pulse control signal is output fromsaid pulse current control circuit.
 2. The pulse MAG arc weldingapparatus according to claim 1 wherein said pulse current settingcircuit comprising:a first pulse current setting circuit for settingremaining three pulse control conditions for said first pulse currentgroup which have not been preselected and for outputting first pulsecurrent group setting signals including setting signals corresponding toremaining said three pulse control conditions other than said pulsecondition control signal; a second pulse current setting circuit forsetting remaining three pulse control conditions for said second pulsecurrent group which have not been preselected and for outputting secondpulse current group setting signals including setting signalscorresponding to said remaining said three pulse control conditionsother than said pulse condition control signal; and said pulse frequencyand width signal generation circuit generates a pulse frequency andwidth signal in response to the pulse frequency control signal and pulsewidth setting signal if the pulse frequency control reference signal isoutput from said pulse condition control signal generation circuit, thepulse frequency signal and pulse width control signal if the pulse widthcontrol signal is output from said pulse condition control signalgeneration circuit, or the pulse frequency signal and pulse widthsetting signal if the peak current control signal or base currentcontrol signal is output from said pulse condition control signalgeneration circuit; and said switching circuit outputs a switchingsignal for alternatively switching between said first and second arcvoltage setting circuits and between said first and second pulse currentsetting circuits.
 3. The pulse MAG arc welding apparatus according toclaim 2 wherein said pulse condition control signal generation circuitgenerates a pulse frequency control reference signals for controllingthe pulse frequency in common with said first and second pulse currentgroups as said pulse condition control signal and said pulse frequencysignal generation circuit generates a pulse frequency signal in responseto said pulse frequency control reference signal input thereto.
 4. Thepulse MAG arc welding apparatus according to claim 2 wherein said pulsecondition control signal generation circuit generates a pulse widthcontrol signal for controlling the pulse width in common with said firstand second pulse current groups as said pulse condition control signaland said pulse frequency and width signal generation circuit outputs apulse frequency and width signal in response to said pulse frequencysignal from said pulse frequency signal generation circuit and saidpulse width control signal from said pulse condition control signalgeneration circuit.
 5. The pulse MAG arc welding apparatus according toclaim 2 wherein said pulse condition control signal generation circuitgenerates a peak current value control signal for controlling the peakcurrent value in common with said first and second pulse current groupsas said pulse condition control signal.
 6. The pulse MAG arc weldingapparatus according to claim 2 wherein said pulse condition controlsignal generation circuit generates a base current value control signalfor controlling the base current in common with said first and secondpulse current groups as said pulse condition control signal.
 7. Thepulse MAG arc welding apparatus according to claim 2 further comprisinga first wire feeding rate setting circuit for outputting a first wirefeeding rate setting signal and a second wire feeding rate settingcircuit for outputting a second wire feeding rate setting signal and awire feeding rate switching circuit for sending a wire feeding ratecontrol circuit a wire feeding rate signal obtained by switching betweensaid first wire feeding rate setting signal and said second wire feedingrate setting signal.
 8. The pulse MAG arc welding apparatus according toclaim 1 wherein said pulse condition control signal generation circuitgenerates a pulse frequency control reference signal for controlling thepulse frequency in common with said first and second pulse currentgroups as said pulse condition control signal and said pulse frequencysignal generation circuit generates a pulse frequency signal in responseto said pulse frequency control reference signal input thereto.
 9. Thepulse MAG arc welding apparatus according to claim 1 wherein said pulsecondition control signal generation circuit generates a pulse widthcontrol signal for controlling the pulse width in common with said firstand second pulse current groups as said pulse condition control signaland said pulse frequency and width signal generation circuit outputs apulse frequency and width signal in response to said pulse frequencysignal from said pulse frequency signal generation circuit and saidpulse width control signal from said pulse condition control signalgeneration circuit.
 10. The pulse MAG arc welding apparatus according toclaim 1 wherein said pulse condition control signal generation circuitgenerates a peak current value control signal for controlling the peakcurrent value in common with said first and second pulse current groupsas said pulse condition control signal.
 11. The pulse MAG arc weldingapparatus according to claim 1 wherein said pulse condition controlsignal generation circuit generates a base current value control signalfor controlling the base current in common with said first and secondpulse current groups as said pulse condition control signal.
 12. Thepulse MAG arc welding apparatus according to claim 1 further comprisinga first wire feeding rate setting circuit for outputting a first wirefeeding rate setting signal and, a second wire feeding rate settingcircuit for outputting a second wire feeding rate setting signal and awire feeding rate switching circuit for sending a wire feeding ratecontrol circuit a wire feeding rate signal obtained by switching betweensaid first wire feeding rate setting signal and said second wire feedingrate setting signal.